Protein coated polymeric substrate

ABSTRACT

The present invention provides a method for the functionalization of a polymeric surface with a protein by physical adsorption. The method enables a membrane spanning protein to be used as an anchor for proteins and/or peptides for display. Also provided are polymeric substrates for protein or peptide display, and related kits and methods of use.

The present invention relates to a method of immobilising a membranespanning protein upon a polymeric substrate. The invention also relatesto a polymeric substrate comprising a membrane spanning proteinimmobilised thereon, wherein the membrane spanning protein serves as ananchor for heterologous peptides and/or proteins. The invention alsorelates to uses of a coated polymeric substrate as described herein; andkits for making a coated polymeric substrate as described herein. Alsoprovided are novel modified membrane spanning proteins as describedherein, and the nucleic acid sequences encoding the same.

BACKGROUND

There is a need for simple, scalable methods for immobilization ofproteins on a variety of materials for many applications e.g. diagnosticbiosensors, immunodiagnostics, surgical implants, and bioprocessingmedia for affinity purification. In all applications it is critical topreserve the protein structure and function, and to orientate itcorrectly on the substrate for maximum efficiency of performance. Thereare numerous strategies for the immobilization of proteins on surfaces,as reviewed in Nakanishi, K. et al. ((2008) Current Proteomics 5:161-175).

Physisorption is a commonly used method based on hydrophobic or ionicinteractions of the protein with the surface. It is methodologicallysimple, but allows little quantitative or orientational control; it mayalter the functional properties of the protein through unfolding, andreproducibility and efficiency are variable. This means that when bound,the proteins may not be oriented correctly for analyte binding or may berendered wholly or partially denatured and non-functional. Many of thesemethods are complicated with many process steps and difficult to scalefor mass manufacture. The methods also result in a large percentage lossof function of the protein concerned; for example less than 10% ofantibody adsorbed to plastic ELISA plates is active whilst chemicalcoupling e.g. amine coupling results in 75-100% loss of activity (ButlerJ. E. et al. (1992) J Immunol Methods 150: 77-90; Butler J. E. et al.(1992) J Immunol Methods 150: 77-90; Esser, P. (2010) Thermo ScientificApplication Note 11 b; Johnsson, B. et al. (1995) J MolecularRecognition 8: 125-131).

Other methods of binding proteins to a surface include functionalizationof the surface, for example via amination or carboxylation to allowcovalent coupling of the proteins to the surface, or coating of thesurface to mediate binding (e.g. streptavidin or biotin coating, polyLyscoating, protein A coating, or nickel coated surfaces). Other methodsinclude modification of the protein by addition of a binding tag (forexample PhaF) which binds to bioplastic PHA derived from bacteria. Suchmethods based on covalent coupling provide a stable linkage, can beapplied to a range of proteins and have good reproducibility. However,orientation may be variable, and chemical derivatisation may alter thefunction of the protein and requires a stable, interactive surface.Biological capture methods utilising a tag (such as hexahistidine/Ni-NTAor biotin/avidin) on the protein provide a stable linkage and bind theprotein specifically and in reproducible orientation, but the partnerreagent must first be immobilised adequately on the surface.

WO2002057780 describes the binding of protein to gold surfaces inself-assembled monolayers where the biologically functional moiety ofthe protein is correctly oriented and retains close to 100% of itsactivity. The technology involves the use of a modified variant of aβ-barrel structured bacterial outer membrane protein (OMP) as a scaffoldupon which other proteins and peptides of interest may be fused. Thescaffold has intrinsic self-assembling properties on gold and is used asthe anchor point for a fusion partner. The fusion partner is correctlyoriented and retains function. The binding of the OMP to the goldsurface relies upon modification of the protein to include a cysteineresidue at an appropriate position in the OMP such that when thecysteine forms a covalent bond with the gold surface the protein iscorrectly orientated and directly coupled to the surface.

These methods have the disadvantage of requiring specific amino acids inthe protein to mediate the reaction with the surface, modifications ofthe surface to accept covalent bonding from the cysteine, and thepresence of amphiphilic molecules such as thiolipids or thioalkanes tostabilise the protein monolayer.

The applications requiring protein attachment to a surface arewidespread, often requiring high protein density across a small area inorder to maximise assay sensitivity. Plastic has many advantages for useas a substrate in protein based assays. However, the hydrophobic natureof plastic surfaces results in non-specific binding and denaturation ofthe proteins.

The present invention aims to overcome or ameliorate some of theproblems associated with the prior art.

BRIEF SUMMARY OF THE DISCLOSURE

In a first aspect of the present invention, there is provided a methodfor immobilising a membrane spanning protein onto a polymeric substrate,the method comprising:

-   -   i) providing a sample of a membrane spanning protein in        detergent;    -   ii) providing a polymeric substrate;    -   iii) incubating the protein sample of i) with the polymeric        substrate of ii); and    -   iv) reducing the detergent concentration of the protein sample        to 1× Critical Micelle Concentration (CMC) of the detergent or        below;        wherein the protein becomes immobilised upon the substrate by        physisorption.

The membrane spanning protein may anchor, or may be modified to anchor,a heterologous protein or peptide for display. Thus, when bound to thepolymeric substrate, the membrane spanning protein is capable ofdisplaying a protein or peptide anchored thereto, preferably in anoriented and functional manner. Thus, an anchored peptide and/or proteinmay be spatially removed from the surface of the polymeric substrate, toaid display. An anchored protein or peptide may be functional.

The membrane spanning protein comprises a head and a foot, the head andfoot being spaced apart from one another by a body comprising one ormore membrane spanning strands. By “anchors” means that the membranespanning protein may comprise a heterologous peptide and/or protein in aloop at the head of the protein and/or at an N and/or C terminus at thehead of the protein. By “modified to anchor” means that the membranespanning protein is engineered to comprise an N and/or C terminus at thehead of the protein, and/or one or more loops at the head of theprotein. A heterologous peptide and/or protein may be provided at anengineered N and/or C terminus at the head of the protein, or in anengineered loop at the head of the protein, for display.

Thus, a the membrane spanning protein of the invention:

-   -   i) comprises a heterologous peptide and/or protein in a loop at        the head of the protein;    -   ii) comprises a heterologous peptide and/or protein at an N        and/or C terminus at the head of the protein;    -   iii) is engineered to comprise an N and/or C terminus at the        head of the protein; and/or    -   iv) is engineered to comprise one or more loops at the head of        the protein.

A heterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display. Preferably, the membranespanning protein comprises a heterologous peptide and/or protein.

A spacer may be provided to create a spatial distance between themembrane spanning protein and the peptide and/or protein for display.

In an embodiment, a protein sample may comprise a detergentconcentration of greater than 1×CMC, for example 1.5×CMC, 2×CMC, 2.5×CMCor higher. The detergent concentration of the protein sample is thatwhich enables the protein to remain in solution. When protein is at highconcentration e.g. 1.5 μM, it precipitates more easily in low detergentconcentration; therefore the protein sample may have a detergentconcentration of about 2×CMC solution in order to keep the proteinsoluble. Binding of the protein to the polymeric substrate is achievedby reducing the detergent concentration to 1×CMC or below. The detergentconcentration is preferably maintained above 0×CMC in order to allow aperiod of time when the protein remains in solution and can bind to thesubstrate. The reduction may be achieved either by dilution or bydialysis, or any other suitable method.

The detergent concentration may be reduced prior to incubation of theprotein sample with the polymeric substrate (step iii). Alternatively,the detergent concentration may be reduced on or after incubation withthe polymeric substrate. Reduction of the detergent concentration of theprotein enables binding of the membrane spanning protein to thepolymeric substrate, wherein a peptide or protein anchored by themembrane spanning protein is preferably functional and orientated fordisplay. Reduction of the detergent concentration enables binding of themembrane spanning protein to the polymeric substrate without requiringmodification of the primary or secondary structure of the protein, ormodification or functionalization of the substrate.

Dilution may comprise the addition of water, a buffer, or any othersuitable diluent. A diluent may comprise a detergent, provided that theeffect of mixing with the diluent is reduction in the concentration ofthe detergent of the protein sample to 1×CMC or below, preferably from0.05×CMC to 1×CMC.

The step of reducing the detergent concentration of the protein samplemay also effectively reduce the protein concentration, for example byincreasing the volume of solution in which the protein is present. Thedilution is sufficient to allow the protein to remain in solution for asufficient period of time to bind the substrate, but the detergentconcentration is low enough to allow physisorption of the protein to thepolymeric substrate.

The method may further comprise washing the substrate.

The method may further comprise sterilising the substrate.

The detergent in which the protein is provided may be any ionic,non-ionic or zwitterionic detergent.

In a second aspect of the present invention, there is provided apolymeric substrate comprising a membrane spanning protein immobilisedthereon, wherein the membrane spanning protein is immobilised upon thesubstrate by physisorption, and wherein the membrane spanning proteinanchors, or is modified to anchor, a heterologous protein or peptide fordisplay.

When bound (i.e. immobilised) to the polymeric substrate, the membranespanning protein is capable of displaying a protein or peptide anchoredthereto in an oriented and functional manner. Thus, a peptide and/orprotein anchored by an immobilised membrane spanning protein may bespatially removed from the surface of the polymeric substrate, to aiddisplay. An anchored protein or peptide may be functional.

The use of the membrane spanning protein overcomes problems in bindingsmall peptides or proteins in a functional and oriented manner to apolymeric substrate, by serving as an anchor for such peptides orproteins. Thus, by displaying the peptide and/or protein on a membranespanning protein which is immobilised on the polymeric substrate, thepeptide and/or protein retains function, structure, and/or may beoriented in a manner which enables interaction with other components.

The membrane spanning protein may be defined as in relation to the firstaspect. Thus, there may be provided a polymeric substrate comprising amembrane spanning protein immobilised thereon, wherein the membranespanning protein is immobilised upon the substrate by physisorption, andwherein the membrane spanning protein:

-   -   i) comprises a heterologous peptide and/or protein in a loop at        the head of the protein;    -   ii) comprises a heterologous peptide and/or protein at an N        and/or C terminus at the head of the protein;    -   iii) is engineered to comprise an N and/or C terminus at the        head of the protein; and/or    -   iv) is engineered to comprise one or more loops at the head of        the protein.

A heterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display. Preferably, the membranespanning protein comprises a heterologous peptide and/or protein.

A spacer may be provided to create a spatial distance between themembrane spanning protein and the peptide and/or protein for display.

The heterologous peptide and/protein may be functional.

Preferably, the membrane spanning protein is immobilised without a crosslinking agent. Thus, the protein is immobilised upon the polymericsubstrate without functionalization or modification of the surface toenable protein binding thereto. Cross linking agents include for exampletags, binding partners for example biotin and streptavidin, protein A,etc.

Preferably, the membrane spanning protein does not comprise modificationto a substrate binding domain, which may be provided in the foot of theprotein. For example, the protein comprises its native primary and/orsecondary sequence in a substrate binding domain. Preferably, themembrane spanning protein may not comprise modifications which enablecovalent binding to the polymeric substrate.

Preferably, the membrane spanning protein is immobilised in the absenceof a stabilizing agent such as a lipid, for example a lipid monolayer.Herein, a stabilising agent does not include a detergent.

Preferably, the membrane spanning protein is a β-barrel protein.Preferably, the membrane spanning protein is a porin, preferably anOuter Membrane Protein (OMP) of gram negative bacteria, more preferablyOmpA or OmpF.

In a third aspect of the present invention, there is a provided aproduct comprising a polymeric substrate comprising a membrane spanningprotein immobilised thereon, wherein the membrane spanning protein isimmobilised upon the substrate by physisorption, and wherein themembrane spanning protein anchors, or is modified to anchor, aheterologous protein or peptide for display.

The polymeric substrate may be defined as in relation to the secondaspect of the invention. Thus, there may be provided a productcomprising a polymeric substrate comprising a membrane spanning proteinimmobilised thereon, wherein the membrane spanning protein isimmobilised upon the substrate by physisorption, and wherein themembrane spanning protein:

-   -   i) comprises a heterologous peptide and/or protein in a loop at        the head of the protein;    -   ii) comprises a heterologous peptide and/or protein at an N        and/or C terminus at the head of the protein;    -   iii) is engineered to comprise an N and/or C terminus at the        head of the protein; and/or    -   iv) is engineered to comprise one or more loops at the head of        the protein.

A heterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display. Preferably, the membranespanning protein comprises a heterologous peptide and/or protein.

In a fourth aspect of the present invention, there is provided a methodof binding a component in a sample, the method comprising:

-   -   i) providing a polymeric substrate comprising a membrane        spanning protein immobilised thereon, wherein the membrane        spanning protein is immobilised upon the substrate by        physisorption, and wherein the membrane spanning protein anchors        a heterologous protein or peptide for display;    -   ii) adding sample to the substrate;    -   iii) maintaining the substrate with sample under conditions to        allow binding of any component to the substrate.

The method may optionally comprise washing the substrate to remove anyunbound material; detecting the presence or absence of bound component;and/or elution of any bound component. The method may be useful inscreening of a sample for a component of interest, or purifying acomponent of interest from a sample, or immobilising a component ofinterest from a sample, for example for further reaction.

The method may comprise immobilising a membrane spanning protein on apolymeric substrate, as described herein.

The membrane spanning protein may be defined as in relation to the firstand further aspects of the invention. The polymeric substrate may bedefined as in the second and further aspects of the invention. Thus, themethod may comprise:

-   -   i) providing a polymeric substrate comprising a membrane        spanning protein immobilised thereon, wherein the membrane        spanning protein is immobilised upon the substrate by        physisorption, and wherein the membrane spanning protein anchors        a heterologous protein or peptide for display;    -   ii) adding sample to the substrate;    -   iii) maintaining the substrate with sample under conditions to        allow binding of any component to the substrate,        wherein the polymeric substrate polymeric substrate comprises a        membrane spanning protein immobilised thereon, wherein the        membrane spanning protein is immobilised upon the substrate by        physisorption, and wherein the membrane spanning protein:    -   i) comprises a heterologous peptide and/or protein in a loop at        the head of the protein;    -   ii) comprises a heterologous peptide and/or protein at an N        and/or C terminus at the head of the protein;    -   iii) is engineered to comprise an N and/or C terminus at the        head of the protein; and/or    -   iv) is engineered to comprise one or more loops at the head of        the protein.

A heterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display. Preferably, the membranespanning protein comprises a heterologous peptide and/or protein.

In a fifth aspect, there is provided a method of mediating aninteraction of an anchored peptide and/or protein with a component in asample, the method comprising:

-   -   i) providing a polymeric substrate comprising a membrane        spanning protein immobilised thereon, wherein the membrane        spanning protein is immobilised upon the substrate by        physisorption, and wherein the membrane spanning protein anchors        a heterologous protein or peptide for display;    -   ii) adding sample comprising a component to the substrate;    -   iii) maintaining the substrate with sample under conditions to        allow interaction of the component with anchored peptide and/or        protein.

The membrane spanning protein may be defined as in relation to the firstand further aspects of the invention. The polymeric substrate may bedefined as in the second and further aspects of the invention. Thus, themethod may comprise:

-   -   i) providing a polymeric substrate comprising a membrane        spanning protein immobilised thereon, wherein the membrane        spanning protein is immobilised upon the substrate by        physisorption, and wherein the membrane spanning protein anchors        a heterologous protein or peptide for display;    -   ii) adding sample comprising a component to the substrate;    -   iii) maintaining the substrate with sample under conditions to        allow interaction of the component with anchored peptide and/or        protein        wherein the polymeric substrate polymeric substrate comprises a        membrane spanning protein immobilised thereon, wherein the        membrane spanning protein is immobilised upon the substrate by        physisorption, and wherein the membrane spanning protein:    -   i) comprises a heterologous peptide and/or protein in a loop at        the head of the protein;    -   ii) comprises a heterologous peptide and/or protein at an N        and/or C terminus at the head of the protein;    -   iii) is engineered to comprise an N and/or C terminus at the        head of the protein; and/or    -   iv) is engineered to comprise one or more loops at the head of        the protein.

A heterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display. Preferably, the membranespanning protein comprises a heterologous peptide and/or protein.

The component may be a cell, such that the peptide and/or protein mayact as an effector for cell growth, development and differentiation. Thepeptide and/or protein may mediate an enzymatic reaction, or may act asa catalyst. For example, the peptide and/or protein may be a growthfactor or signalling protein, or may induce cellular processes such assignalling pathways etc.

It is envisaged that a polymeric substrate of the present invention mayanchor two or more different peptides and/or proteins via one or moremembrane spanning proteins, for example to provide different functionssimultaneously. Thus, for example, a combination of cell-attachment andgrowth factors may be provided on a substrate.

In a sixth aspect of the present invention, there is provided a surgicalimplant comprising a polymeric substrate comprising a membrane spanningprotein immobilised thereon, wherein the membrane spanning protein isimmobilised upon the substrate by physisorption, and wherein themembrane spanning protein anchors, or is modified to anchor, aheterologous protein or peptide for display.

The membrane spanning protein may be defined as in relation to the firstand further aspects of the invention. The polymeric substrate may bedefined as in the second and further aspects of the invention.

In a seventh aspect of the present invention, there is provided anincubation comprising a polymeric substrate, a membrane spanningprotein, and detergent at a concentration of 1×CMC or below. This aspectof the invention relates to an intermediate in the production of apolymeric substrate of the invention. Any suitable method may be usedfor reduction of the detergent concentration, as described herein. It isenvisaged that some of the membrane spanning protein may be immobilisedon the substrate in the incubation. Preferably, the membrane spanningprotein anchors, or is modified to anchor, a heterologous protein orpeptide for display. Preferably, the membrane spanning protein becomesimmobilised upon the substrate by physisorption. The membrane spanningprotein may be defined as in relation to the first and further aspectsof the invention. The polymeric substrate may be defined as in thesecond and further aspects of the invention.

In an eighth aspect of the present invention, there is provided a kitcomprising a polymeric substrate, and a membrane spanning protein whichanchors, or is modified to anchor, a heterologous protein or peptide fordisplay. The membrane spanning protein may be defined as in relation tothe first and further aspects of the invention. The polymeric substratemay be defined as in the second and further aspects of the invention.

In a ninth aspect of the present invention, there is provided a membranespanning protein, which anchors, or is modified to anchor, aheterologous protein or peptide for display. The membrane spanningprotein comprises a head and a foot, the head and foot being spacedapart from one another by one or more membrane spanning strands. By“anchors” means that the membrane spanning protein may comprise aheterologous peptide and/or protein in a loop at the head of the proteinand/or a heterologous peptide and/or protein at an N and/or C terminusat the head of the protein. By “modified to anchor” means that themembrane spanning protein is engineered to comprise an N and/or Cterminus at the head of the protein, and/or one or more loops at thehead of the protein.

Preferably, the membrane spanning protein:

-   -   i) comprises a heterologous peptide and/or protein in a loop at        the head of the protein;    -   ii) comprises a heterologous peptide and/or protein at an N        and/or C terminus at the head of the protein;    -   iii) is engineered to comprise an N and/or C terminus at the        head of the protein; and/or    -   iv) is engineered to comprise one or more loops at the head of        the protein.

A heterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display. Preferably, the membranespanning protein comprises a heterologous peptide and/or protein. Amembrane spanning protein may be a protein as defined herein, forexample an OMP protein as defined Table 7.

In a tenth aspect of the invention, there is provided a nucleic acidsequence encoding a membrane spanning protein, wherein the membranespanning protein anchors, or is modified to anchor, a heterologousprotein or peptide for display. The membrane spanning protein may bedefined as in relation to the first and further aspects of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are further described hereinafter withreference to the accompanying drawings, in which:

FIG. 1 shows the design of plastic binding β-barrel proteins based onthe directed evolution of the β-barrel scaffold protein OmpA. OMP0 isthe original gold-binding modified version of OmpA that has truncated N-and C-termini, a 6×His tag for affinity purification and a cysteine atthe ‘foot’ of the protein for covalent bonding to gold.

FIG. 2 shows the detection of immobilized P24 antigen and P24-fusionproteins on polystyrene plates (A, B) and Polysorp plates (C, D) withanti-HIV1-P24 (A, C) and Anti-HIV1/2 P24 (B, D) monoclonal antibodies.

FIG. 3 shows the culture of MG63 bone cells on 96 well polystyreneplates coated with a range of OMP proteins displaying differentbiological properties. Blank represents an unmodified polystyrene welland OMP154 is the umodified scaffold protein, the addition of the 4amino acids RGDS to OMP154 creates OMP153 a protein able tosignificantly enhance cell attachment.

FIG. 4 is a schematic diagram of IgG-binding functional assay for OMP18and Native Protein A. The OMP18 structure is shown in the figure. Instep 1, the protein is attached to the plastic surface; in step 2 IgG isbound to any functional IgG-binding domains; in step 3 and anti-IgGantibody conjugated to alkaline phosphatase that cannot bind to theProtein A domains is bound to any IgG already on the surface; and instep 4 a colorimetric enzymatic reaction is carried out to discernsurfaces that have immobilized IgG.

FIG. 5 shows the results of immunoassay to test for presence offunctional protein on surfaces. These data clearly demonstrate thatimmobilization of Protein A IgG-binding domains fused to an OMP betabarrel scaffold anchor retains much greater function on plasticsurfaces. The scale of the advantage was unexpected and this isespecially marked on the hydrophobic surface compared to the hydrophilicsurface. Even on the hydrophilic surface the OMP18 protein shows muchgreater functionality than native protein A.

FIG. 6 shows poly lactic acid polymer 3D printed into open lattice 3Ddiscs. The discs were treated with OMP0 (umodified OmpA) and OMP5 (OMP0engineered to display the FLAG epitope). After protein treatment all thesurfaces could be tested with an alkaline phosphatase conjugatedanti-FLAG antibody to quantify protein attachment.

FIG. 7 shows the detection of FLAG epitope with alkaline phosphataseconjugated antibody and PNPP. Error bars represent standard deviation.Note that OmpA here refers to OMP0. Similar levels of non-specificbinding were seen on the no protein and OMP0 treated surfaces withsignificantly more antibody binding to the OMP 5 treated surfaces.

FIG. 8 shows DAPI stained PC12 cells grown on; A. OMP36 treated polymerfibres, B. Protein-free fibres. Both images captured using 10× objectivelens.

FIG. 9 shows the attachment and growth of 3T3 fibroblasts on OMP36treated plates.

FIG. 10 shows a comparison of OMP FGFs coated on polystyrene to solubleFGF2 in the media.

FIG. 11 Alignment of OMP59 and OMP171. The extracellular loops and longC-terminus present on OMP59 but deleted from OMP171 are shown as dottedlines on the OMP171 sequence. The alpha helical spacer sequence is shownin italics with the mutated residues in OMP171 underlined. Two extrahydrophilic residues unique to the C-terminus of OMP171 are shown inbold and the cysteine residue is indicated by a *.

FIG. 12 is a schematic figure showing the structures of the proteinstested in this experiment.

FIG. 13 Alignment of the amino acid sequences of OMP0 and OMP154. Theelongated Loop 1 is shown in italics on the OMP154 sequence. The loopsthat were deleted in OMP154 and the truncated C-terminal tail are shownas a dotted line on the OMP154 sequence. The insertion site for smallmotifs is shown by the black triangle. The cysteine present in OMP0 hasbeen mutated to a Glycine in OMP154 (underlined).

FIG. 14 shows the nucleic acid and amino acid sequence of OMP0“wild-type” modified by removal of signal and C-terminal domain andaddition of N-terminal his tag and cysteine at position 10. TM1 isresidues 49-84; OL1 is residues 85-126; TM2 is residues 127-165; TM3 isresidues 175-213; OL2 is residues 214-249; TM4 is residues 250-285; TM5is residues 301-345; OL3 is residues 346-387; TM6 is residues 388-427;TM7 is residues 436-465; OL4 is residues 466-507; TM8 is residues508-540; Cysteine is residues 28-30. TM—transmembrane strand (one passthrough the membrane), OL—outer loop (extracellular loop).

FIG. 15 shows the nucleic acid and amino acid sequence of OMP 9 Loop 1circular permutation.

FIG. 16 shows the nucleic acid and amino acid sequence of OMP 13 Loop 3circular permutation.

FIG. 17 shows the nucleic acid and amino acid sequence of OMP 14 Loop 4circular permutation.

FIG. 18 shows the nucleic acid and amino acid sequence of OMP 140 shortloops, alpha helical spacer, c-terminal his tag, no cysteine.

FIG. 19 shows the nucleic acid and amino acid sequence of OMP 154 OMP0with short loops and truncated C-term, but loop 1 elongated.

FIG. 20 shows the nucleic acid and amino acid sequence of OMP170 shortloops, n-terminal his tag, cysteine at aa 122.

FIG. 21 shows the nucleic acid and amino acid sequence of OMP171, as 170but with alpha helical spacer after his tag.

FIG. 22 shows the immobilisation of protein at different detergentconcentrations. The OMP18 protein (at a final 0.1 μM) was diluted in thedetergent concentration shown in 96 well plates. One set of wells waswashed and dried after 6 h whereas adsorption was allowed to proceed for24 h in the second set of wells. After washing the surfaces were probedwith mouse IgG and detected with anti-mouse AP conjugate and PNPPsubstrate colorimetric reaction. The best result was obtained with OMP18in DM at 0.125×CMC adsorbed for 24 h.

FIG. 23 shows the degree of saturation of the protein on the substrate.Effect of OMP18 concentration. Omp18 was diluted to different finalconcentrations in detergent at 0.125× CMC and adsorbed for 24 h. MouseIgG binding assay was carried out as described herein. The resultsdemonstrate that the surface was almost saturated at 100 nM (0.1 μM)protein in all the detergents and this was chosen as the standardconcentration for adsorption.

FIG. 24 is a scan of OMP9 and OMP18 spotting experiment. White paperplugs were placed in each well to obtain a clear scan of the bottom ofthe well.

FIG. 25 shows a hypothetical 6 stranded barrel protein. Circularpermutation results in repositioning of the N- and C-termini and thebeta strand.

FIG. 26 shows SDS PAGE analysis of samples from polybead experiment. 5μL of human serum loaded in Lane 1, all other lanes 20 μL out of a 1 mLsample loaded. HSA is human serum albumin. V_(H) is the heavy chain ofIgG at ˜50 kDa and V_(L) is the light chain at ˜25 kDa. The samples werein SDS loading dye with 1 mM DTT and heated for 5 min at 95° C.

FIG. 27 shows the 0% SDS wells were washed with SDW. All washes carriedout in triplicate and data shown is the average of three wells. There isa very high reading of greater than 3 A₄₀₅ units because the reactionwith the PNPP substrate solution was allowed to carry on for 15 min.

FIG. 28 shows the detection of OMP203 and OMP18 after washing withTween™. Tween 20 was used.

FIG. 29 shows the effect of washing frequency on immunoassay signal.Tween™ 20 was used. The incubation with PNPP was carried out for 5 minat room temperature.

FIG. 30 shows data from immunoassay after washing with various agents asshown under the x-axis.

FIG. 31 shows the absorbance readings from detection of OMP203.

FIG. 32 shows results of culture of MG63 cells on polystyrene coatedwith OMP proteins displaying various ECM motifs.

FIG. 33 is an electron micrograph of the porous 3D structure of Alvetex.

FIG. 34 shows results of detection of alkaline phosphatase conjugatedIgG on 3D polystyrene treated with OMP proteins.

FIG. 35 shows antibody detection of the OMP proteins on PLA afterseveral days immersion 1% triton X-100.

FIG. 36 shows data from the dynamic light scattering experiments. Theplot shows the change in average particle size over the course of 1hour.

FIG. 37 shows the result of immunoassay of OMP203 detection afterpre-dilution.

DETAILED DESCRIPTION

The present invention is based upon a different approach to thefunctionalization of a polymeric surface with a protein by physicaladsorption. The method of the present invention enables theimmobilisation of a membrane spanning protein onto a polymeric substratewithout requiring covalent binding, and yet retaining the advantages ofphysisorption i.e. not requiring chemical modification of either theprotein or the substrate, and not requiring the presence of stabilisingcompounds such as thiolipids and thioalkanes. The method of the presentinvention enables a membrane spanning protein to be used as an anchorfor proteins and/or peptides for display. The anchored peptides and/orproteins, because they are not immobilised directly to the polymericsurface, retain function and/or structure, and are oriented for display.Thus, the membrane spanning proteins are bound to the substrate in amanner which enables their use as an anchor for display.

The present invention enables a membrane spanning protein to beimmobilised upon a polymer substrate i) non-covalently (for example byVan der Waals interactions or ionic bonding); ii) without modificationto a substrate binding domain (e.g. the foot) of the membrane spanningprotein (e.g. modification to the primary or secondary structure) toinclude a substrate binding residue; iii) without functionalization ormodification of the substrate to enable membrane spanning proteinbinding thereto; and/or iv) in the absence of a stabilizing agent suchas a lipid. Further, the method of the present invention enables iv) themembrane spanning protein to anchor a peptide and/or protein fordisplay, preferably such that the peptide and/or protein is functionaland oriented for display. Preferably an anchored peptide and/or proteinis directed away from the surface of the polymeric substrate, such thatit is available for display.

The highly hydrophobic nature of membrane spanning proteins means thatthey precipitate in solution unless stabilized by high concentration ofdetergent (above 1×CMC, preferably 2×CMC). This also prevents suchproteins from binding to surfaces. It was expected that the presence ofdetergent would prevent binding of the protein by hydrophobicinteractions to a surface, and immobilization would be inefficient atbest. Unexpectedly, however, it was found that dilution of the proteinin low detergent concentration enabled immobilisation of the membranespanning protein to a polymeric surface, in a manner which enabledfunctional and orientated display of an anchored peptide and/protein.The immobilisation of membrane spanning proteins to a polymericsubstrate according to the invention is distinct from immobilisationmethods of the prior art. Surprisingly, the inventors have shown thatthe method of the invention results in a large increase in functionalitywhen the protein is anchored to the surface by the membrane spanningprotein. The great advantage of the present invention is exemplified bythe fusion of an HIV antigen (the P24 protein) to a membrane spanningprotein (the OMP170-type scaffold) as shown in FIG. 2.

Herein, a substrate comprises a surface to which a protein can beimmobilised. The substrate may take any suitable form which can receiveprotein for immobilisation thereon. A substrate is preferably solid(i.e. not a gel or a liquid). A substrate may comprise a smooth surfaceor may be textured. The substrate, or a surface thereof, may be a mesh,a fibre, a bead, knitted or woven fabric, a well or micro-well plate, atissue culture flask, or any other surface. The substrate comprises apolymer material, at least on a binding surface thereof. A substrate maycomprise one or more different polymers. The substrate preferablycomprises a bare polymer surface, meaning that it has not been coatedwith other material (e.g. proteins such as biotin or streptavidin) toaid binding of protein to the substrate or has not been functionalised,for example by amidation or carboxylation to mediate binding.

Polymers (polymeric substrates) may include plastic, silk and otherproteinaceous fibres (for example hair, fur (keratin filaments), actinfilaments, collagen filaments etc.), and graphene. A polymer may be aplastic. Plastics will be known to persons skilled in the art, and mayinclude polyvinyl, polyethylene (PE) including for example polyethyleneterephthalate (PET) and high-density polyethylene (HDPE) and low-densitypolyethylene (LDPE), polyacrylate (acrylic), polystyrene (PS) includinghigh impact polystyrene (HIPS), silicone, polyester (for examplepolylactic acid (PLA) or polylactic coglycolic acid (PGLA)),polyurethane, polypropylene (PP), polyamide (nylon), Acrylonitrilebutadiene styrene (ABS), Polyethylene/Acrylonitrile Butadiene Styrene(PE/ABS), bakelite, rubber, latex, polycarbonate (PC),Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS) and polyvinylchloride including for example polyvinylidene chloride (PVDC). Thepolymer may be natural or synthetic. In addition to the organic polymersof which the substrate is made, it may comprise non-organic or organicadditives, from 10-50% by weight. A polymer may be biodegradeable.

A polymeric substrate may be hydrophobic, hydrophilic, or amphiphilic,or a combination of two or more thereof. In an embodiment, at least partof a polymeric substrate is hydrophobic.

Herein, a membrane refers to a cell membrane (also known as a plasma orcytoplasmic membrane) which surrounds a cell to separate the inside ofthe cell from the surrounding environment. The term membrane hereinincludes both inner and outer membranes. The term “extramembranous”refers to beyond the membrane, for example the extracellular,periplasmic or cytoplasmic space, as appropriate. Reference herein toperiplasmic, cytoplasmic or extracellular is made with respect to thenative positioning of the protein in the membrane. A cell membranecomprises a phospholipid bilayer, in which are embedded proteins toassist in communication and transport across the cell membrane. Thus, aprotein which spans the membrane as defined herein is one which spansthe phospholipid bilayer.

By a heterologous peptide or protein is meant that the peptide orprotein moiety is not naturally associated with the product referred to,in nature. It may also be referred to as being foreign. Thus, ananchored peptide or protein sequence or a spacer may be heterologous toa membrane spanning protein, meaning that these peptides and/or proteinsare not found in the membrane spanning protein in nature.

An engineered protein or nucleic acid sequence is one which has beenmodified by the hand of man, for example using recombinant protein orDNA technology to provide a nucleic acid sequence or protein which isdifferent in primary, secondary or tertiary sequence to the nativenucleic acid or protein sequence. A protein may be engineered to bespatially different to the native protein, which may also be describedas an engineered secondary or tertiary structure.

In the present invention, a peptide or protein is a string of aminoacids which are connected by peptide bonds. A protein may also bereferred to as a polypeptide. Amino acids can be natural, non-natural,or a combination thereof. They may be L-amino acids or D-amino acids.Peptides and proteins may be chemically synthesised or purified fromnatural or recombinant sources. Proteins may have a secondary structure,and optionally a tertiary structure. Peptides on the other hand describeshort, linear amino acid chains which generally lack secondary ortertiary structure. A peptide may comprise 2 or more amino acidresidues. A protein may comprise 20 or more amino acid residues.

The term “nucleic acid sequence(s),” as used herein, means a single ordouble-stranded deoxyribonucleotide or ribonucleotide polymer of anylength but preferably at least 15 nucleotides, and include asnon-limiting examples, coding and non-coding sequences of a gene, senseand antisense sequences complements, exons, introns, genomic DNA, cDNA,pre-mRNA, mRNA, rRNA, siRNA, miRNA, tRNA, ribozymes, recombinantpolypeptides, isolated and purified naturally occurring DNA or RNAsequences, synthetic RNA and DNA sequences, nucleic acid probes, primersand fragments.

Herein, a membrane spanning protein refers to a protein which in itsnative form resides in a cell membrane, and spans the membrane. Amembrane spanning protein may also be referred to herein as an integralmembrane protein or a transmembrane protein. A membrane spanning proteincomprises a head and a foot which are spatially separated by a bodycomprising one or more membrane spanning strands. By “spanning” is meantthat it extends across at least most of a lipid bilayer of a cellmembrane. Thus, “membrane spanning” for the purposes of the presentinvention may include proteins which extend beyond the membraneboundaries or do not extend fully across the membrane boundaries. Theymay be distinguished from proteins which are able to travel across themembrane, but do not span a membrane as defined herein. A membranespanning protein may be a single pass protein, meaning that it spans themembrane once, or may be a multi-pass protein, meaning that it spans themembrane one or more times. A membrane spanning protein may comprise oneor more polypeptides. Typically, in its native form a membrane spanningprotein may have role in transport across a cell membrane, ion exchange,cell signalling or communication, as a linker or enzyme and in membranebiogenesis.

By “pass” is meant a span of the membrane by the protein, or asubstantial span of the membrane. Therefore, a single pass protein willspan the membrane once, having an N terminus at either the head or foot,and a C terminus at the other. Therefore, a single pass protein will nothave an extramembranous loop. A 2-pass protein will span the membranetwice, such that both N and C termini protrude from the head or foot. A2 pass protein will comprise a single turn or loop. Alternatively,membrane spanning proteins may be referred to as X-stranded proteins,meaning that they have a defined number of strands which span the lipidbilayer. Herein, when referring to spans across the lipid bilayer, theterms “pass” and “strand” may be used interchangeably.

A membrane spanning protein will by its nature comprise a secondarystructure, such that it is of a size and shape that it would reside in,and span the membrane as defined herein. The term therefore would notinclude short peptide sequences or linear sequences substantiallylacking in secondary structure. Further, it is expected that a proteinwhich is anchored to a membrane and which predominantly reside outsideof the membrane would not be suitable for use in the present invention.Those skilled in the art will appreciate that the term“membrane-spanning” should not be interpreted strictly so as to excludefrom this invention proteins extending partially beyond the membraneboundaries or extending only across the majority of the region betweenthe membrane boundaries.

Membrane spanning proteins may comprise an alpha-helical structure. Suchmembrane spanning proteins may be found in the inner membranes ofbacterial cells or the plasma membrane of eukaryotes, and sometimes inthe outer membranes. The majority of membrane spanning proteins arealpha-helical. Membrane spanning proteins may alternatively comprise abeta-barrel configuration. Such proteins are found in the outermembranes of Gram-negative bacteria, the cell wall of Gram-positivebacteria, and outer membranes of mitochondria and chloroplasts. Amulti-pass membrane spanning protein may comprise joins (for exampleturns) which link units of secondary structure (for examplebeta-strands). Such joins may be exposed to an aqueous phase, such asthe cytosol periplasm or extracellular fluid.

A membrane spanning protein as described herein will aggregate in water.

A membrane spanning protein of the present invention may be naturallyoccurring or may be recombinant. A membrane spanning protein of thepresent invention may be engineered.

Preferred membrane spanning proteins for use in the present inventionare those comprising a beta barrel structure. A beta barrel proteincomprises a large beta-sheet, which adopts hollow, cylindrical structureor barrel shape. In the beta barrel, beta strands of the beta sheet arearranged in an anti-parallel manner, although some beta-barrel proteinshave been identified comprising parallel strands. Hydrophobic residuesmay be oriented toward the exterior of the barrel, and hydrophilicresidues facing the interior. Adjacent beta strands in a beta barrel maybe adjacent in sequence (referred to as an “up and down beta barrel) ornon-adjacent in sequence (referred to as a Greek key or a Greek-keybarrel). A beta barrel protein may comprise any number of strands, forexample from 8 to 22 beta strands. A beta barrel protein may comprise aneven number of beta strands or an odd number of beta strands.

The adjacent strands or helices of a membrane spanning protein such as abeta barrel are each linked by a turn or a loop. A turn is an element ofa secondary structure in a protein, where the amino acid chain changesdirection. Turns include tight turns (including α, β, γ, δ and π-turns),multiple turns, hairpin turns. A turn is typically defined by the natureof the hydrogen bonding between residues of the turn. Turns, inparticular β-turns, are typically found at the periplasmic end of amembrane spanning protein. A β-turn may also be referred to as a β-bendor a tight turn. A β-turn is a region of a protein where the polypeptidechain folds back on itself by about 180°. A turn may comprise 2 to 6amino acid residues, more preferably 4 amino acids of a β-turn. A β-turnmay comprise proline and glycine residues. Each turn in a beta-barrelprotein may be numbered, for example T1, T2 and so on. Typically, turnsare not extramembranous. A loop of a membrane spanning protein istypically longer than a turn, and may extend out of the membrane intothe extramembranous space. Loops show high sequence variability, andgenerally lack secondary structure. A loop may be hydrophilic in nature,compared to a membrane spanning portion of a membrane spanning protein(e.g. a beta-strand or barrel structure) which may typically behydrophobic in nature. Loops may be denoted L1, L2 etc.

A membrane spanning protein will typically comprise turns on one side ofa membrane, and loops on the other. The end of the protein comprisingmostly loops is referred to herein as the head of the protein. The endof the protein comprising mostly turns is referred to herein as the footof the protein. In outer membrane proteins (i.e. of gram negativebacteria, chloroplasts and mitochondria), the loops are generally allfound on one side of the protein which faces the extracellular space.Herein, this is the head of an outer membrane protein. The endcomprising the turns and termini generally faces the periplasmic space,and is referred to herein as the foot of the protein. One or more alphahelical strands span the membrane, forming the body of the protein. Ininner membrane protein or eukaryotic membrane proteins, loops may befound on the periplasmic or cytoplasmic facing end of the protein. Thehead is therefore defined herein as that end comprising extramembranousdomains, for example the majority of loops. The foot is that whichpredominantly comprises turns, with less extramembranous domains thanthe other end of the protein.

The N and C termini are the ends of the protein, the C terminuscomprising a free carboxyl (COOH) and the N terminus comprising a freeamino (NH2) group. Herein, reference to the terminus includes referenceto the end N or C residue, or the N or C terminal tail, or a partthereof. For a membrane spanning protein, a tail is that portionadjacent the N or C terminus which protrudes from the membrane i.e. itis the portion between a membrane spanning strand and an N or C terminalresidue. The tail may comprise 2 or more amino acid residues, forexample 2, 5, 10, 15, 20, 30, 40, 50 or more amino acid residues. Thetails of the OmpA protein are shown in FIG. 14 as residues 17 to 48 (Nterminal) and 180 to 207 (C terminal). In a preferred embodiment,engineering of the protein comprises permuating a loop of the protein tocomprise the N and/or C terminal tail, preferably wherein the tailcomprises the sequence of amino acids 17 to 48 (N terminal) and/or 180to 207, or a part thereof.

The membrane spanning protein may be an integral membrane protein,preferably a beta-barrel protein, preferably a porin. The membranespanning protein may be an ion-channel, a receptor for a ligand, anenzyme, or other.

Beta barrel proteins include porins, which natively function astransporters for ions and other small molecules which are unable todiffuse across a cell membrane. Loops are provided between beta strands.Porins include Outer Membrane Proteins (OMP) of Gram-negative bacteria,which are porins of the outer membrane. These include OmpA also known asOmpII, an eight-stranded β-barrel, and OmpF which is a homotrimer of 16stranded β-barrels (also referred to as Porin ompF Outer membraneprotein 1 A). Other beta-barrel proteins include preprotein translocasespresent in mitochondria and chloroplasts; and lipocalins.

A membrane spanning protein for use in the present invention may beeukaryotic or prokaryotic. It may be bacterial. It may be plant-derived,or mammalian.

Membrane spanning proteins for use in the present invention will beavailable to persons skilled in the art. Examples of known beta barrelproteins for use in the present invention include: (Curr Opin Struct.Biol 2011 Aug. 21(4) 523-531):

8 stranded proteins: Ail of Yersinia pestis (PDB ID: 3QRA, 3QRC); NspAof Neisseria meningitides (1P4T); OmpA of E. coli (1 QJP, IBXW, 1G90,2GE4, 2JMM); OmpA of Klebsiella pneumonia (2K0L); OmpA of Legionellapneumophila (3LDT); OmpW of Escherichia coli (2F1V, 2F1T); OmpX ofEscherichia coli (1QJ8, 1ORM, 1Q9F, 1Q9G, 1QJ9); OprG of Pseudomonasaeruginosa (2×27); PagP of Escherichia coli (1MM4, 1MM5, 3GP6, 1THQ);PagL of Pseudomonas aeruginosa (2ERV); TtoA of Thermus thermophiles(3DZM);

10 stranded proteins: OmpT of Escherichia coli (1178); OpcA of Neisseriameningitides (1K24, 2VDF); Pla of Yersinia pestis (2X55, 2X56);

12 stranded proteins: EspP of Escherichia coli (2QOM); EstA ofPseudomonas aeruginosa (3KVN); Hbp of Escherichia coli (3AEH); Hia ofHaemophilus influenza (2GR8); LpxR of Salmonella typhimurium (3FID);IcsA of Shigella flexneri (3ML3); NaIP of Neisseria meningitidis (1 UYN,1UYO); NanC of Escherichia coli (2WJQ, 2WJR); OMPLA of Escherichia coli(1QD5, 1QD6, 1FW2, 1FW3, 1ILD, 1ILZ, 1IMO); OprM of Pseudomonasaeruginosa (1WP1); ToIC of Escherichia coli (1EK9); Tsx of Escherichiacoli (1TLW, 1TLY, 1TLZ); VceC of Vibrio cholera (1YC9);

14 stranded proteins: α-HL of Staphylococcus aureus, (7AHL, 3M2L, 3M3R,3M4D, 3M4E); FadL of Escherichia coli (1T16, 3DWN, 2R4L, 2R4N, 2R40,2R4P, 2R88, 2R89, 2R8A, 1T1L); FadL of Pseudomonas aeruginosa (3DWO);OmpG of Escherichia coli (2F1C, 2IWV, 2IWW, 2JQY, 2WVP, 2X9K); TbuX ofRalstonia pickettii (3BRY); TodX of Pseudomonas putida (3BS0, 3BRZ);

16 stranded proteins: FhaC of Bordetella pertussis (2QDZ, 2NJT); MspA(1UUN); Omp32 of Comamonas acidovorans (1E54); Omp32 of Delftiaacidovorans (2FGQ, 2FGR); OmpK36 of Klebsiella pneumonia (1OSM); OmpC ofEscherichia coli (2J1N, 2J4U, 2XE1, 2XE2, 2XE3, 2XE5, 2XG6); OmpF ofEscherichia coli (2ZFG, 1BT9, 3FYX, 1GFM, 1GFN, 1GFO, 1GFP, 1GFQ, 3HW9,3HWB, 1HXT, 1HXU, 1HXX, 3K19, 3K1B, 1MPF, 300E, 2OMF, 2OPF); OprP ofPseudomonas aeruginosa (204V); PhoE of Escherichia coli (1 PHO); Gdp^(a), Rhodobacter capsulatus, (2POR); Gdp^(a) , Rhodopseudomonas blastica,(1H6S, 1PRN, 2PRN, 3PRN, 5PRN, 6PRN, 7PRN, 8PRN); PorB, Neisseriameningitidis, (3A2R, 3A2S, 3A2T, 3A2U); ^(a)Gdp—general diffusion porin.PDB IDs are provided in parenthesis. Further information for the PDB IDslisted can be found at the Protein Data Bank (www.rcsb.org).

18 stranded protein: BenF of Pseudomonas fluorescens pf-5, (3JTY); LamB,Escherichia coli, (1MPM, 1MPN, 1MPO, 1MPQ, 1AF6, 1MAL); LamB, ofSalmonella typhimurium, (2MPR); OpdK of Pseudomonas aeruginosa, (2QTK);OprD, of Pseudomonas aeruginosa (2ODJ); or ScrY of Salmonellatyphimurium, (1A0T, 1A0S, 1OH2);

19 stranded proteins: VDAC1 of Mus musculus (3EMN); VDAC1 of Homosapiens (2K4T, 2JK4)

22 stranded proteins: BtuB of Escherichia coli (1NQE, 1NQF, 2GUF, 2GSK,1NQG, 1NQH, 1UJW, 2YSU, 3M8B, 3M8D); Cir of Escherichia coli (2HDI,2HDF); FauA of Bordetella pertussis (3EFM); FecA, Escherichia coli(1KMO, 1PNZ, 1KMP, 1PO0, 1PO3); FepA, Escherichia coli (1 FEP); FhuA,Escherichia coli (1 BY3, 1 BY5, 1 FCP, 2FCP, 1 FI1, 2GRX, 1QFF, 1QFG,1QJQ, 1QKC); FptA, Pseudomonas aeruginosa (1XKVV); FpvA, Pseudomonasaeruginosa (2W75, 2O5P, 2W16, 2W6T, 2W6U, 2IAH, 2W76, 2W77, 2W78, 1XKH);HasR, Serratia marcescens (3CSL, 3CSN, 3DDR); ShuA, Shigelladysenteriae, transporter (3FHH); and

24 stranded proteins: PapC of Escherichia coli (3FIP)

Herein, the term “OMPXX” or “ORLAXX” where X is a numerical value havebeen used in relation to preferred scaffolds for use in the presentinvention. The terminology “OMP” is not limiting, and any suitablemembrane spanning protein as defined herein may be modified as describedin relation to any of the specific “OMPXX” or “ORLAXX” scaffolds toachieve the present invention. A preferred membrane spanning protein foruse in the present invention is OMP of E. coli as described herein, andpreferably the OMP0 of FIG. 14. Further preferred membrane spanningproteins are any one of the OMPXXs defined in Table 7. The presentinvention includes within its scope membrane spanning proteins modifiedas described in relation each “OMPXX” specifically, and uses methods andproducts comprising such proteins as described herein.

Suitable membrane spanning proteins may be identified by analysis of thesecondary structure. Protein secondary structure is defined byinter-residue hydrogen bonds, which result in the formation of athree-dimensional structure. Secondary structure includes α-helices,β-sheets, and various turns, depending upon the number and type ofresidues and the resulting bonding. Amino acids vary in their ability toform secondary structure, enabling the secondary structure of a peptideor protein to be predicted from the amino acid sequence. Any suitableprediction method may be used in the present invention to identifymembrane spanning proteins, in particular beta-barrel proteins, from theprimary structure (For example see: Barton (1995) Current opinion instructural biology Vol 5 p 372-376; Jones (1999) Journal of MolecularBiology Vol 292 p 195-202; Pirovano and Herringa (2010) Chapter 19:Protein Secondary structure prediction. In: Methods in MolecularBiology—Data Mining Techniques for the life sciences Eds. O Carugo and FEisenhaber, Humana Press DOI 10.1007/978-1-60327-241-4). Such methodsmay also be used in the present invention during modification of amembrane spanning protein to predict folding, and therefore secondarystructure, of a modified or synthetic protein sequence.

The Critical Micelle Concentration (CMC) is defined as the concentrationof detergents above which micelles are spontaneously formed. Atconcentrations above the CMC, the detergents form complexes withlipophilic proteins. Below the CMC, detergents merely partition intomembranes without solubilizing membrane proteins. The highly hydrophobicnature of the β-barrel core of membrane spanning proteins means thatthey precipitate in solution unless stabilized by high concentration ofdetergent (greater than 1×CMC). This also prevents such proteins frombinding to surfaces.

The CMC will vary depending upon the detergent, for example SDS has aCMC of 7-10 mM; dodecylmaltoside has a CMC of 0.15 mM; octylglucosidehas a CMC of 20-25 mM. Therefore, a detergent concentration for SDS of7-10 mM is expressed as 1×CMC. A detergent concentration of 0.3 mM ofdodecylmaltoside is expressed as 2×CMC, and so on.

The dilution factor will depend on the starting concentration of theprotein and the detergent in the sample, and the required workingconcentration after dilution, and can be calculated by a person skilledin the art based using known dilution techniques to provide a CMC of1×CMC or below, and a protein concentration where it retains solubilityin that concentration of detergent for sufficient time to bind to thesubstrate. Whether or not a protein is soluble can readily be determinedby a person skilled in the art, using available solubility assays. If aprotein is insoluble it will precipitate and form a cloudy solution. Theturbidity can be measured, for example by measuring the absorbance at400 nm. Alternatively, a simple visual assessment can be used to detecta cloudy solution, indicating a protein which is no longer soluble.

The method of the present invention comprises reducing the detergentconcentration of the protein sample of i) to 1×CMC or below. Preferably,the CMC is maintained above 0. Thus, the CMC may be reduced to from0.05×CMC to 1×CMC, 0.075×CMC to 1×CMC, preferably 0.1×CMC to 1×CMC, orfrom 0.05×CMC to 0.9×CMC, 0.075×CMC to 0.9× CMC, preferably 0.1×CMC to0.9×CMC, or from 0.05×CMC to 0.8×CMC, 0.075×CMC to 0.8×CMC, preferably0.1×CMC to 0.8×CMC, or from 0.05×CMC to 0.7×CMC, 0.075× CMC to 0.7×CMC,preferably 0.1×CMC to 0.7×CMC, or from 0.05×CMC to 0.6×CMC, 0.075×CMC to0.6×CMC, preferably 0.1×CMC to 0.6×CMC, or from 0.05×CMC to 0.5× CMC,0.075×CMC to 0.5×CMC, preferably 0.1×CMC to 0.5×CMC, or from 0.05×CMC to0.4×CMC, 0.075×CMC to 0.4×CMC, preferably 0.1×CMC to 0.4×CMC, or from0.05×CMC to 0.3×CMC, 0.075×CMC to 0.3×CMC, preferably 0.1×CMC to0.3×CMC, or from 0.05×CMC to 0.2×CMC, 0.075×CMC to 0.2×CMC, preferably0.1×CMC to 0.2×CMC.

Preferably, these values are the detergent concentration of incubationmixture after the protein sample has been incubated with the polymericsubstrate, although it is envisaged that the reduction in detergentconcentration may be performed prior to incubation. Within theseparameters, protein is prevented from precipitating into particulates insolution but instead is encouraged to attach to the polymeric substrate.

The appropriate dilution factor for any particular detergent may bedetermined readily by the skilled person, by testing the degree ofsaturation of a substrate with a membrane spanning protein anchored to apeptide and/or protein for display, and the solubility of the proteinwhen incubated with the substrate. A suitable dilution factor providesat least 60%, 65%, 70%, 75%, 80%, 85%, 90% or at least 95% saturation ofthe substrate, and the protein remains in solution for at least 6 hours,preferably at least 8 hours, preferably at least 10 hours, and mostpreferably overnight (i.e. 12-24 hours). Saturation can be determinedusing a binding assay as described below.

Any suitable detergent may be used. Preferred detergents are those whichstabilise the protein and prevent it from precipitating out of solutionbut allow the protein to interact with and bind to the substrate. Mostpreferably, the detergent may be selected from the group consisting ofn-octylglucoside, dodecylmaltoside or Thesit. A detergent may be usedalone, or in combination with one or more other detergents, preferablyselected from those defined above. Preferably, the same detergent isused for both adding to the protein to provide a protein sample, andwhere detergent is used in the dilution in combination with a diluent.

Suitable buffers include phosphate buffers, Tris buffers, HEPES buffers,MES buffers, TES buffers, glycine buffers, acetate buffers, and anyother buffers recognised as such by those skilled in the art.

The protein may be provided in solution, or as a dried product.Preferably, the protein is provided in a buffer, to which detergent isadded. Where the protein is provided as a dried product, the method maycomprise the additional step of dissolving the protein in a suitablebuffer for example ROG-8 (50 mM Tris HCl, 0.1 mM EDTA, 1% OG).

In the method of the present invention, the detergent concentration ofthe protein sample may be reduced prior to incubation with thesubstrate. Additionally or alternatively, the detergent concentrationmay be reduced after incubation of the sample and substrate. In anembodiment, a diluent may be added to the substrate prior to incubationwith the sample, which effectively reduces the detergent concentrationof the sample upon incubation. Thus, step ii) may comprise adding adiluent to the polymeric substrate prior to incubating the substratewith the protein.

Thus, the method may comprise:

-   -   i) providing a sample of a membrane spanning protein in        detergent;    -   ii) providing a polymeric substrate;    -   iii) adding a diluent to the polymeric substrate such that upon        addition of protein sample there is provided a CMC of 1× or        below;    -   iv) incubating the protein sample of i) with the polymeric        substrate of iii);    -   wherein the protein becomes immobilised upon the substrate by        physisorption.

The method may comprise:

-   -   i) providing a sample of a membrane spanning protein in        detergent;    -   ii) providing a polymeric substrate;    -   iii) reducing the detergent concentration of the protein sample        such that when incubated with the substrate the CMC is 1× or        below;    -   iv) incubating the protein sample of iii) with the polymeric        substrate of ii);        wherein the protein becomes immobilised upon the substrate by        physisorption.

The protein may be added to the substrate in any suitable manner, forexample it may be patterned (e.g. spotted).

The incubation is preferably carried out at room temperature or below(but above 0° C.). Preferably, the incubation is maintained for at least6, preferably at least 8 hours, preferably at least 10 hours, and mostpreferably 12-24 hours. 24 hours is the optimum incubation period. In anembodiment, the method further comprises washing the substrate. Thesubstrate may be washed with any suitable buffer, water, or solutionscontaining detergent or ethanol for example TBS, PBS, HEPES, TE, 70%ethanol, Tween, or deionised water, preferably sterile. Washing has thepurpose of removing from the substrate any unbound material and anyresidual detergent. The substrate may be dried. It may further besterilised. It may be packaged for sale.

Binding of the membrane spanning protein to the substrate can bedetermined using any suitable method in the art, including for example abinding assay. In a typical binding assay, the substrate may beincubated with a ligand (for example, IgG) which is able to bind abinding site of the membrane spanning protein, or to a peptide orprotein anchored thereby. Any unbound ligand is removed by washing.Bound ligand may then be detected, either directly for example if itcomprises a signal which can be measured, or indirectly, for example byusing a second binding member specific for the ligand. The secondbinding member may be an antibody conjugated to enzyme or catalyst orother marker such as a fluorescent tag, and detection may be performedby incubation with a substrate and measuring the amount of signalproduced. Any suitable signal may be used, many examples of which willbe known and available to persons skilled in the art. Preferred signalsare those that can be detected in the electromagnetic spectrum, such aschromophores and fluorophores, and enzyme substrate systems such asHorseradish peroxidase/TMB. Others will be known to persons skilled inthe art. In the latter case, a binding member specific for the ligandmay be bound to an enzyme, which catalyses the signal substrate toproduce a colorimetric output. Preferred signals are those which employan amplification system. Enzyme labels which can act on a substrate toproduce chromophores are most preferred, e.g. Horseradish Peroxidase,alkaline phosphatase, beta galactosidase. Suitable substrates includeTMB ABTS, OPD (for HRP), pNPP (for AP) and ONPG (for betagalactosidase).

The signal generated provides an indication of the degree of binding ofthe membrane bound protein to the substrate (i.e. the degree ofsaturation of the substrate) and whether any peptide or protein anchoredthereto is not denatured, and is available for ligand binding. Bysaturated is meant that the maximum amount of protein is bound to thesubstrate, i.e. the substrate is fully occupied.

Thus, the method of the present invention provides a polymeric substratecomprising a membrane spanning protein immobilised thereon, wherein themembrane spanning protein is immobilised upon the substrate byphysisorption, and wherein the membrane spanning protein anchors, or ismodified to anchor, a heterologous protein or peptide for display.

By “immobilised” is meant that the protein is bound to the substrate,and remains bound after washing with water and/or a buffer containingdetergent (for example Tween 20 at 0.05% (w/v)).

The membrane spanning protein may be provided on the substrateuniformly, or in a predetermined pattern, for example spotting. Thepresent invention may also comprise a method of patterning a surface,comprising application of a membrane spanning protein of the inventionto a substrate in a pattern. Preferably the pattern is pre-determined.Suitable methods of patterning a surface include lithography, inkjet,droplet injections and other methods known to persons skilled in theart.

Physisorption is physical adsorption of a compound to a surface, bynon-covalent binding, for example van der waals interactions,hydrophobic interactions, charge interactions. Physisorption is not achemical reaction between the protein and the substrate and is anon-covalent binding.

The present inventors have shown that, unexpectedly, a membrane spanningprotein can be bound to a polymeric substrate by physisorption, and becapable of displaying an anchored peptide or protein. Thus, method ofthe invention enables a membrane spanning protein to be immobilised on apolymeric substrate, and to serve as an anchor to display a peptideand/or protein which may be functional and oriented for display. Thisbinding of the membrane spanning protein to the substrate and itseffectiveness as an anchor for peptides and/or proteins which aredisplayed in a functional and oriented manner means that the polymericsubstrate has utility in a binding assay, as well as in othermethodologies. The present invention therefore provides for the firsttime a polymeric substrate having a membrane spanning proteinimmobilised thereon, wherein the membrane spanning protein anchors, oris modified to anchor, a heterologous protein or peptide for display.

By anchor is meant that the membrane spanning protein may comprise aheterologous peptide and/or protein in a loop at the head of the proteinand/or a heterologous peptide and/or protein at an N and/or C terminusat the head of the protein. Thus, the membrane spanning protein binds oris fused to a peptide or protein, which is displayed at the head of themembrane spanning protein. Thus, the membrane spanning protein andpeptide and/or protein may be expressed as a single polypeptide chain.

By modified to anchor means that the membrane spanning protein isengineered to comprise an N and/or C terminus at the head of theprotein, and/or one or more loops at the head of the protein, to enableit to display a peptide or protein when immobilised on the substrate.Thus, a peptide or protein may be displayed at the head of the protein.The modification enables an anchored protein or peptide to be isspatially removed from the surface of the substrate, and preferably isnot sterically hindered by the membrane spanning protein or the surface.Thus, the anchored peptide or protein may be functional, and availablefor binding or other interaction. The engineering to provide an N and/orC terminus at the head of the protein may be achieved by circularpermutation. This circular permutation means that the order of featuresof the protein is altered, without substantial impact on the overalltertiary structure of the protein. This may be achieved by engineeringof the primary structure of the membrane spanning protein, usingtechniques available in the art. Thus, a membrane spanning protein maybe engineered for an N and/or C terminus to extend from the head of theprotein rather than the foot. A terminus, may be engineered to beprovided in place of a loop, or adjacent to a loop, from within a loop.In an embodiment, an N or C terminal is engineered to extend from aloop. This may be achieved by engineering a loop to include an N and/orC terminus. Preferably, where both N and C termini are permutated, theymay be engineered to be provided in the same loop. Thus, part of a loopmay form an N terminus and part of a loop may for a C terminus. In sucha situation, the loop is split, forming two domains rather than a loopstructure. Thus, all or part of a loop may be replaced by an N and/or Cterminus. Where the protein is OMP, the loop may be loop 1, 3 or 4. Whenimmobilised on the substrate, the engineered terminus extends away fromthe surface of the substrate, providing an effective display site for aprotein or peptide. A spacer may also be provided on the end of one orboth termini, to further aid in display of an anchored peptide orprotein thereto.

In an embodiment, a loop or N or C terminus may comprise a spacersequence which serves to spatially distance a peptide or protein linkedthereto from the substrate.

The heterologous peptide and/or protein is anchored for display by themembrane spanning protein. This means that is provided in the membranespanning protein at a position such that when immobilised on thesubstrate, the peptide and/or protein is spatially distanced from thebinding surface of the substrate, and as such is available for access bya component of interest (for example, in a binding reaction).Preferably, by anchored for display means that it is spatially distancedfrom steric hindrance with a membrane spanning protein which may preventits interaction with a component of interest. Display of a heterologouspeptide or protein can be ascertained using detection assays asdescribed herein.

An anchored protein preferably retains any secondary structure, thusenabling it to retain function. By “retains its secondary structure”means that substantially all anchored protein (i.e. at least 70%, 75%,80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% of the bound protein) has itsnative, secondary structure. The native secondary structure of theprotein is the folded structure under non-denaturing conditions. Whilstit is envisaged that some denaturation of the protein may occur uponbinding, the overall secondary structure of the protein is substantiallythe same as the native secondary structure, and any denaturation doesnot have a significant effect on the overall folding of the protein, orits ability to bind a ligand. Secondary structure may also be referredto herein as conformation.

Where a heterologous peptide is inserted into a loop of the membranespanning protein, it is preferably provided in a long loop, betweenmembrane spanning strands. It is preferably provided toward the middleof the loop. The loop may be truncated prior to insertion of the peptidesequence. The loop may be lengthened in addition to insertion of thepeptide sequence, for example by a spacer. Alternatively, the peptidesequence may be introduced into a native loop, so that it is lengthenedcompared to its native form. The modified loop may be longer or shorterthan the native loop. When inserted into a loop, a heterologous peptidemay be any suitable length, but preferably is too short to adopt asecondary structure which may interfere with the secondary structure ofthe membrane spanning protein. For example, suitable lengths may be from3 to 70 amino acids. A heterologous peptide sequence may be provided inthe N terminus, the C terminus, or both. A heterologous sequence(peptide or protein) may be independently provided at the end of aterminus, or within the sequence forming the terminus. Preferably, it isprovided at the N terminus, preferably at the end of the N terminus. Aterminus may be engineered as described herein to provide an anchor(display) site for a peptide or protein.

By functional means that the peptide and/or protein retains one or moreof its native functions, for example a binding function, a receptorfunction, a signalling function, or an enzymatic function.

The membrane spanning protein comprises a head and a foot, the head andfoot being spaced apart from one another by a body comprising one ormore membrane spanning strands. By “anchors” means that the membranespanning protein may comprise a heterologous peptide and/or protein in aloop at the head of the protein and/or a heterologous peptide and/orprotein at an N and/or C terminus at the head of the protein. By“modified to anchor” means that the membrane spanning protein isengineered to comprise an N and/or C terminus at the head of theprotein, and/or one or more loops at the head of the protein. Aheterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display.

Thus, the membrane spanning protein may:

-   -   i) comprises a heterologous peptide and/or protein in a loop at        the head of the protein;    -   ii) comprises a heterologous peptide and/or protein at an N        and/or C terminus at the head of the protein;    -   iii) be engineered to comprise an N and/or C terminus at the        head of the protein; and/or    -   iv) be engineered to comprise one or more loops at the head of        the protein.

A heterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display.

A heterologous peptide may be any peptide sequence, preferably afunctional peptide sequence. A peptide sequence may consist of, bederived from or function as: a growth factors, a protein or peptideinvolved in protein-protein interaction or binding, an antibody bindingmotif, an epitope, an antigen, an allergen, an enzyme, a catalyst, aprotein or a peptide involved in interactions or binding with DNA and/orcarbohydrate; a protein or peptide involved in interaction or bindingwith small molecules, (drugs etc), cell binding, or cell signaling; anextracellular matrix protein; and indeed any other protein or peptidewhich may be desirable to display on a polymeric surface, for anypurpose. Specific examples of peptides and proteins for use in theinvention include binding sites for a protein, for example a FLAGepitope (DYKDDDDK); a growth factor such as FGF1 or FGF2, interleukin,thrombopoietin (TPO), stem cell factor (SCF), granular macrophage colonystimulating factor (GMCSF), Leukocyte inhibitory factor (LIF), sonichedgehog (Shh); cell binding motifs for example of extramembranousmatrix proteins such as integrin, collagen, laminin or fibronectin (e.g.as described in Table 3); extracellular matrix (ECM) protein motifs, forexample RGDS, antigens (e.g HIV (e.g.) p24 antigen, BMP-2, vitronectin,osteopontin, Tenascin-C), and indeed any others known to persons skilledin the art. The peptide sequence may comprise any combination of two ormore such peptide sequences.

Preferably, the peptide or protein may be a growth factor. The peptideor protein may be of any growth factor. A preferred growth factor isFGF1 or FGF2. In an embodiment, a growth factor may be anchored to thefusion protein, preferably directly to an N or C terminus of themembrane spanning protein. Preferably, a spacer may be provided betweenthe membrane spanning protein and the growth factor. The provision of aspacer enables the growth factor and membrane spanning protein to refoldindependently upon expression. In addition, the spatial separation ofthe growth factor from the membrane spanning protein enables the growthfactor to extend above the polymeric surface and to be functional as agrowth factor without steric hindrance by the membrane spanning protein.The provision of a growth factor on a polymeric surface has particularapplication in cell culture techniques, for example to promote cellgrowth and/or differentiation.

The use of a spacer sequence in combination with a heterologous peptideand/or protein improves display of a peptide or protein, by orientatingit away from the polymeric substrate. The provision of a spacer may alsoenable a heterologous protein and membrane spanning protein to refoldindependently upon expression, thus increasing the possibility ofobtaining a functional heterologous peptide or protein anchored to themembrane spanning protein. The spatial separation provided by a spacerenables a heterologous peptide or protein to extend above the polymericsurface and to be functional without steric hindrance by the substrateor membrane spanning protein. A spacer may be provided in a loop, and/orat the end of an N and/or C terminus. A spacer may be in turn fused to apeptide or protein, for example for binding. Thus, the N and/or Cterminus may be used for display of larger sequences, as the samerestrictions regarding the effect of secondary structure are less likelyto apply. A spacer may be heterologous to the membrane spanning proteinand/or to the peptide and/or protein. A spacer may be an alpha helicalsequence, anchored at one end to the free end of an N or C terminus,preferably an N terminus. A spacer may be provided in a loop, preferablyadjacent to a heterologous peptide or protein. A spacer may behydrophilic, rigid or semi rigid. A spacer may comprise any suitableprimary or secondary sequence, but preferably lacks function such assignally, binding or other function. A preferred spacer may comprise analpha helix, or a PT linker, for example as described in Poon et al, JBiol Chem 282: 2091-2011 2006, or a glycine-serine spacer linker forexample PLrigid, 2aa GS linker, 6aa [GS]× linker, 10aa [GS]× linker, 10aa flexible protein domain linker, 8 aa protein domain linker, Splitfluorophore linker; Freiburg standard, 15 aa flexible glycine-serineprotein domain linker; Freiburg standard, Short Linker(Gly-Gly-Ser-Gly), Middle Linker (Gly-Gly-Ser-Gly)×2, Long Linker(Gly-Gly-Ser-Gly)×3, GSAT Linker, SEG, SEG-Linker, GSAT-Linker,Z-EGFR-1907Short-Linker, Z-EGFR-1907Middle-Linker,Z-EGFR-1907Long-Linker, Z-EGFR-1907_SEG-Linker, (Gly4Ser)3 FlexiblePeptide Linker, Short Fusion Protein Linker: GGSG with standard 25prefix/suffix, Long 10AA Fusion Protein Linker with Standard 25Prefix/Suffix, Medium 6AA Fusion Protein Linker: GGSGGS with Standard 25Prefix/Suffix. (http://parts.igem.org/Protein_domains/Linker). An alphahelical sequence may be provided for fusion to a heterologous peptide orprotein, for example as shown in OMP173 of FIG. 12.

The present invention has the advantage that the membrane spanningprotein is bound to the substrate in a manner which enables binding of abinding partner to a heterologous peptide or protein provided in an Nand/or C terminus or a loop. This is in contrast to methods of the priorart in which the protein is typically bound to the substrate in adisorganised manner or requires additional agents to hold the proteinsin place (for example, lipid monolayers), such that binding is possible.In the present invention, surprisingly, substantially all the anchoredpeptide and/or protein is orientated in a manner which enables it to bedisplayed for binding or interaction. Thus, in the present invention atleast 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% of the anchoredpeptide and/or protein is oriented away from the polymeric substratesurface, and is displayed for binding or interaction. This can beascertained using a binding assay or other techniques available in theart, as described herein, for example as described herein with regard toverification of binding to the substrate.

The N and/or C terminus of the membrane spanning protein may bemodified. For example, one or both of the N or C terminus may betruncated, for example to increase hydrophobicity, or to introduce aheterologous sequence as described above.

Other modifications to the membrane spanning protein basic structure toimprove binding properties may be made. These include: the deletion oflarge internal or external domains that are not integral to themembrane; the truncation of one or more loops to reduce thehydrophilicity of the barrel; elongation of one or more loops, forexample with hydrophilic spacers to allow the insertion and display ofproteins on the loops; circular permutation to alter the spatialpositioning of the N- and/or C-termini; introduction of purificationtags (e.g. his tags, FLAG-tags and others). One or both of the N or Cterminuses may be modified to include one or more amino acid deletions,substitutions or insertions, to alter the structural and/or functionalproperties thereof. One or more loops of the membrane spanning proteinmay be engineered, as described herein.

It may be desirable to increase the hydrophobicity of a protein, forexample by truncating one or more loops of the protein, which aretypically hydrophilic. This may serve to improve binding of the proteinto a hydrophobic substrate, without the requirement forfunctionalization of the plastic surface, or modification of the proteinto introduce binding moieties such as specific amino acids for covalentbinding to the substrate. The shortening of one or more of the long,hydrophilic loops of a membrane spanning protein further has theadvantage of reducing non-specific binding from serum or other matrixproteins, in an assay.

The hydrophobicity of a protein is a measure of the tendency of aprotein to aggregate and repel water. The hydrophobicity of a protein isa factor of the amino acids present in the primary structure, but also afactor of the secondary structure. Therefore, different parts of aprotein may be hydrophobic or hydrophilic. Various methods exist forcategorising the hydrophobicity of amino acid residues, includingchromatographic methods, accessible surface area methods, partitioningmethods. The value may be referred to as the hydropathy index. Ahydropathy plot or X ray structure analysis may be used to predict thehydrophobicity over the length of an amino acid sequence. The scale isbased upon the hydrophobic and hydrophilic properties of the 20 aminoacids. A moving “window” of from 5 to 20 amino acids determines thesummed hydropathy at each point in the sequence (Y coordinate). Thesesums are then plotted against their respective positions (X coordinate)(Kyte and Doolittle Jol Mol. Bio. (1982) 157 105-132). In embodimentswhere it desired to alter the hydrophobicity of a membrane spanningprotein, for example in order to aid binding of the protein to apolymeric substrate, a hydropathy plot may be useful in predicting thehydrophobicity of a loop before and after any modification, to determinewhether a proposed modification results in the desired change inhydrophobicity. In embodiments for example it may be desirable toincrease the hydrophobicity of a protein, for example by truncating oneor more loops of the protein, which are typically hydrophilic.

Membrane spanning proteins for use in the present invention are thosewhich comprise at least one loop, and therefore span the membrane atleast twice. A membrane spanning protein for use in the presentinvention may comprise two or more loops. Each loop of a membranespanning protein may differ in length and structure from one or moreother loops of the protein. Where it is desired to modify a protein, anyone more loops may be truncated as described herein for example toincrease the hydrophobicity of the protein, and enable directedimmobilisation to a hydrophobic substrate. The number of loops which aretruncated will depend upon the protein and the extent to whichhydrophilicity resulting from the loops is desired to be reduced. Thismay be a factor of the specific sequence and length of any particularloop. Using primary sequence analysis, and optionally methods such as Xray crystallography and hydropathy plotting, a skilled person can assessthe predicted hydrophilic/hydrophobic nature of an loop and of amodified membrane spanning protein to determine the appropriate loop(s)to be truncated, and by how many amino acids. Methods are available inthe art for determining hydrophobicity including solvent phasepartitioning, RPLC, TLC. A preferred method includes analysis of theX-ray structures and predictive hydropathy plots (Kyte and Doolittle) tomake decisions when engineering the protein.

The number of loops to be truncated may be defined by number, based onthe native configuration of the protein with the C terminus residing onthe periplasmic side. In a 2 or 3 or more pass protein, 1 or more loopsmay be truncated. In a preferred embodiment, all but one of the loopsmay be truncated. The numbering of the loops herein is based upon thenative C terminus being on the cytosolic side.

By “truncated” is meant that the loop is reduced in length compared toits native form. A reduction in length is achieved by deletion of one ormore amino acid residues from the loop. The extent to which a loop istruncated will depend upon factors such as the degree of hydrophobicityto be achieved by modification of the protein, and the impact of thedeletion on the tertiary structure of the protein. Thus, by “truncated”means that all or part of a loop may be removed. Preferably, a modifiedmembrane spanning protein according to the invention retains its nativetertiary structure. Thus, where the membrane spanning protein is abeta-barrel protein, the modified protein preferably retains abeta-barrel tertiary confirmation. Thus, preferably the shortening orremoval of one or more loops does not significantly impact the finaltertiary structure of the protein compared to its native form. Each loopin a protein may be modified differently to one or more other loops inthe protein, or in the same way as one or more other loops in theprotein. Preferably, a loop is truncated to a length which enables it toconnect transmembrane strands without constriction and preferablywithout altering of the tertiary structure of the protein. Preferably, aloop is truncated such that it does not extend into the aqueous phaseoutside of the membrane.

The truncation of one or more loops of a membrane spanning protein asdescribed herein serves to increase the hydrophobicity of the protein,and also to reduce non-specific binding to the protein. In the presenceof detergent, the protein is able to bind to a hydrophobic substrate.Thus, the protein is immobilised directly to the polymeric substrate,without requirement for tags, functionalization or linker sequences.Preferably, the head is directed away from the polymeric substrate, andas such is available for binding, for example in a screening assay.Preferably, when immobilised to a substrate the protein maintains itssecondary and tertiary structure, and preferably is correctly orientatedfor display of a binding site. Preferably, the protein is functional.Preferably, the protein is orientated for, and capable of, binding to ananalyte or ligand. Preferably, the protein is organised non-randomly onthe surface of the substrate, such that a plurality of proteins areorientated in substantially the same manner. Preferably, the protein ispositioned on the substrate such that any functional sites, such asbinding sites, are exposed, preferably directed toward thesolution/reaction surface.

A loop which is retained in the modified membrane spanning protein maybe modified to include hydrophilic residues, either by insertion orsubstitution. The purpose of introducing hydrophilic residues into theloop is to create repulsion from a hydrophobic substrate and positionthe loop and its active content above the surface such that it isaccessible. Such hydrophilic residues may be part of a spacer peptide orin addition thereto.

The protein may be modified to include a tag, for example apolyhistidine tag. A polyhistidine tag may comprise 6 or more histidineresidues. The tag may be referred to herein as a His6 tag, a 6×his tagor a hexa-his tag. Other suitable tags include FLAG, c-myc or othersmall affinity tag. A tag may be provided on a C or N terminus. Theterminus may be modified as described herein. The tag may be provided ona truncated C or N terminus.

The protein may be modified to remove one or more native cysteineresidues, in particular in those parts of the protein which are tocontact the polymeric substrate. Thus, one or more of the loops may bemodified to remove (by deletion or substitution) one or more nativecysteine residues. Such a modification may be appropriate for proteinswhich are to be bound to plastic substrates, and are not required toexhibit dual functionality of binding to plastic and other substratessuch as gold.

In addition to the modifications described above, a membrane spanningprotein may be modified to include one or more conservativesubstitutions of one or several amino acids without significantlyaltering the biological activity and/or tertiary structure of theprotein. A person skilled in the art will be aware of methods for makingsuch amino acid substitutions.

OmpA is an β-pass protein, meaning that it comprises 8 beta strandswhich form a barrel shape and each span the membrane.

In an embodiment, OmpA may be modified to comprise 3 truncatedextracellular loops. Preferably, each loop is truncated to the length ofa turn, preferably a beta-turn of 4 amino adds. In an embodiment, 3 ofthe 4 extracellular loops are truncated. Loop 1 is retained and modifiedwith a PT linker and hydrophilic amino acids (See FIG. 14). In anembodiment, the remaining loop is lengthened. Preferably, theextracellular loop is lengthened by the introduction of hydrophilicresidues. Preferably, the loop is lengthened by the introduction of apeptide spacer sequence and/or hydrophilic residues. This protein isreferred to herein as OMP154. Variants of OMP154 are described in Table3.

A modified membrane spanning protein may comprise a FLAG epitope(DYKDDDDK) in extracellular loop 1. An OmpA modified in this mannerreferred to herein as OMP5.

A modified membrane spanning protein may comprise the YIGSR motif fromlaminin in extracellular loop 1. This protein is referred to herein asOMP36.

A modified membrane spanning protein may comprise i) all extracellularloops truncated, preferably each truncated to the length of a beta-turn;ii) the N and C termini positioned on the extracellular end (head) ofthe protein; iii) the N terminus modified to include an alpha helicalspacer sequence; iv) a cysteine residue to enable binding of the proteinto a gold surface. This protein is able to bind gold and plasticsubstrates. Preferably, the protein backbone is circularly permuted betabarrel of OmpA (FIG. 14). Preferably, the alpha helical spacer is amutated form of the S. aureus Protein A B domain which does not bind toIgG (the sequence of which is disclosed in Kim et al. (2010) Journal ofexperimental medicine Vol. 207 p 1863-1870). This protein is referred toherein as OMP171. A version lacking the alpha helical spacer is referredto herein as OMP170. A modified version of such a membrane spanningprotein is provided wherein a protein is fused to the spacer. In anembodiment, the protein is HIV antigen p24, and the protein is referredto herein as OMP173.

In an embodiment, a modified membrane spanning protein comprises i) allextracellular loops truncated, preferably each truncated to the lengthof a beta-turn; ii) the N and C termini positioned on the extracellularend (head) of the protein; iii) the N terminus modified to include analpha helical spacer sequence; iv) a His tag provided on the C terminus,v) the protein is free of cysteine residues. These modifications allowthe fusion of large growth factors that contain numerous cysteineresidues and help ensure that only full length expressed proteinscontain the His-tag. Preferably, the protein backbone is a circularlypermuted beta barrel of OmpA. This protein is referred to herein asOMP140. Variants of OMP140 are described in Table 4. OMP90 and128-comprise FGF1 and 2 in an OMP59 scaffold (OMP59 is OMP9 with analpha-helical spacer, is shown in FIG. 11).

In an embodiment, a modified membrane spanning protein comprises i) theN and C termini positioned on the extracellular end of the protein; iii)the N terminus truncated and fused to the IgG binding domain of ProteinA of Staphylococcus aureus. These modifications allow the fusion of theprotein to the Fc region of an antibody to the protein. This protein isreferred to herein as OMP18.

In an aspect of the present invention, there is provided a membranespanning protein which anchors, or is modified to anchor, a heterologousprotein or peptide for display. The membrane spanning protein comprisesa head and a foot, the head and foot being spaced apart from one anotherby one or more membrane spanning strands. By “anchors” means that themembrane spanning protein may comprise a heterologous peptide and/orprotein in a loop at the head of the protein and/or a heterologouspeptide and/or protein at an N and/or C terminus at the head of theprotein. By “modified to anchor” means that the membrane spanningprotein is engineered to comprise an N and/or C terminus at the head ofthe protein, and/or one or more loops at the head of the protein.

Preferably, the membrane spanning protein:

-   -   i) comprises a heterologous peptide and/or protein in a loop at        the head of the protein;    -   ii) comprises a heterologous peptide and/or protein at an N        and/or C terminus at the head of the protein;    -   iii) is engineered to comprise an N and/or C terminus at the        head of the protein; and/or    -   iv) is engineered to comprise one or more loops at the head of        the protein.

A heterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display. Preferably, the membranespanning protein comprises a heterologous peptide and/or protein.

The present invention includes variant membrane spanning proteins to amembrane spanning protein of the invention. Preferably, variant proteinsmay differ in the primary sequence, but retain substantially identicalsecondary tertiary structure to the modified membrane spanning proteinof the present invention. By substantially identical means that theprotein shares at least 40%, preferably 50%, 60%, 70%, 80%, 90%, 95%,96%, 97%, 98% or 99% sequence identity over a suitable window, forexample of 10 to 500 amino acids. Peptide or protein sequence identitycan be determined by methods available in the art, for example usingBLASTP (from the BLAST suite of programs, version 2.2.5 [November 2002])in bl2seq, which is publicly available from NCBI(ftp://ftp.ncbi.nih.gov/blast/); EMBOSS-needle (available athttp:/www.ebi.ac.uk/emboss/align/) and GAP (Huang, X. (1994) On GlobalSequence Alignment. Computer Applications in the Biosciences 10,227-235); Clustal W (Thompson et al 1994, Nucleic Acid Res 11(22)4673-4680.

In a preferred embodiment, a membrane spanning protein is as describedherein. Preferably, it is OmpA.

The modifications to the membrane spanning proteins may be introduced byany suitable technique, many of which will be known to persons skilledin the art. For example, recombinant DNA technology may be used tointroduce modifications to the nucleic acid sequence encoding themembrane spanning protein, which is expressed as a modified membranespanning protein. Recombinant DNA techniques are provided in Sambrook(Sambrook, J. and Russell, D. W. (2001) Molecular cloning. A LaboratoryManual. CSHL Press).

In an aspect of the invention, there is provided a nucleic acid sequenceencoding a modified membrane spanning protein as described herein. Anucleic acid sequence encoding a membrane spanning protein may beengineered to provide a modified membrane spanning protein as describedherein.

OmpA is encoded by a gene which is known in the art as OmpA, con, tolG,and tut. The locus name is b0957 and JW0940. The nucleic acid sequenceencoding OmpA is disclosed in the genome sequence of E. coli(http://bmb.med.miami.edu/sources/1), and herein at FIG. 14. Thesequence shown in FIG. 14 is an engineered form of the wild type gene.The sequence encoding the extracellular loops is underlined.Extracellular loop L1 is encoded by nucleic acids 85-126; L2 is encodedby nucleic acids 214-249; L3 is encoded by nucleic acids 346-387; L4 isencoded by nucleic acids 466-507. The C terminal proline is encoded bynucleic acids 589-591. The N terminal methionine is encoded by nucleicacids 1-3. The sequence intervening loops encodes the membrane spanningbeta strands, as described in Table 1.

OmpF (also known as TOLF or CMLB or COA or CRY or B0929) may also beused in the present invention.

The present invention includes variant nucleic acid sequences encoding amembrane spanning protein of the present invention. The sequenceidentity of a variant or functionally equivalent sequence to a sequenceencoding a membrane spanning protein of the invention is determined bycomparing the two aligned sequences, or fragments thereof, over apre-determined comparison window, and determining the number ofpositions at which identical residues occur. The comparison window maycomprise all or part of the sequence, for example a window comprising10, 20, 30, 40, 50, 100, 200, 500 or 1000 nucleotides or more.Typically, sequence identity is expressed as a percentage. Themeasurement of sequence identity of a nucleotide sequence is a methodwell known to those skilled in the art, using computer implementedmathematical algorithms such as ALIGN (Version 2.0), GAP, BESTFIT, BLAST(Altschul et al J. Mol. Biol. 215: 403 (1990)), FASTA and TFASTA(Wisconsin Genetic Software Package Version 8, available from GeneticsComputer Group, Accelrys Inc. San Diego, Calif.), and CLUSTAL (Higginset al, Gene 73: 237-244 (1998)), using default parameters.

Preferably, a nucleic acid molecule is provided in a genetic construct,which may be used for expression of a modified membrane spanning proteinof the invention, for example in a host cell.

Preferably, the nucleic acid molecule is operably linked to a regulatoryelement, which is any nucleic acid sequence which regulates expression(i.e. transcription or translation) of a coding sequence to which it isoperably linked. Regulatory sequences include promoters, enhancers,transcription terminators, initiation codons, splicing signals includingacceptor and donor splice sites, stop codons, amber or ochre codons,transcription factor binding sites, ribosome binding sites, IRES, andtargeting sequences such as cell compartmentalisation signals (e.g. tothe cytosol, nucleus, plasma membrane, endoplasmic reticulum,mitochondria, chloroplast, lysosome, endosome or Golgi apparatus),and/or secretion signals. Other regulatory sequences may be known topersons skilled in the art. A genetic construct of the invention maycomprise any one or more (two, three, four, five, six etc) regulatorysequences. One or more regulatory elements may be provided in a 5′ UTR.Additionally, a 3′ UTR may also be provided.

A promoter with reference to the present invention may be defined as acontrol sequence that directs transcription of a nucleic acid. Apromoter includes necessary nucleic acid sequences near the start siteof transcription, such as, in the case of a polymerase II type promoter,a TATA element. A promoter may optionally include distal enhancer orrepressor elements that can be located as much as several thousand basepairs from the start site of transcription. Both constitutive andinducible promoters are included for use in the present invention.

Any constitutive or inducible promoter can be used. Common examples ofpromoters used for heterologous gene expression in E. coli are tac, trp,lac, T7, ara omp, lambda phage; but any promoter may be used to expressthese fusions proteins. In contrast to inducible promoters, constitutivepromoters function under most environmental conditions. Many differentconstitutive promoters can be utilized with respect to the methods ofthis disclosure. Preferred promoters for use in the present inventioninclude T7, ara, and tac.

A nucleic acid molecule of the invention may be operably linked to aselectable marker. Where a nucleic acid molecule is provided in agenetic construct, the construct may comprise a selectable marker. Inembodiment, the selectable marker may be operably linked to the nucleicacid molecule. Alternatively, the selectable marker may be controlledindependently to the nucleic acid molecule, for example under thecontrol of a separate promoter and/or other regulatory elements.

Suitable selection markers will be well known to those skilled in theart, and may include any nucleic acid sequence which, upon expression,provides a detectable phenotype. Typically, the expressed polypeptide isdetectable within the cell, preferably without adversely affecting thecell. For example, the selection marker may be green fluorescent proteinor an enzyme, such as luciferase which generates a signal when contactedwith a suitable agent. Other selective markers include those whichconfer upon the cell a selective ability to grow in certain conditions,for example in the absence of specified nutrients, or in the presence ofan agent which would otherwise be adverse to the cell. Preferredselectable markers for use in the present invention include ampicillin,chloramphenicol, kanamycin and tetracycline resistance but others willbe known and available to persons skilled in the art.

Suitable genetic constructs for use in the present invention includevectors including for example viral vectors, plasmids (circular orlinear), phagemids, linear DNA. Preferred genetic constructs for use inthe present invention include plasmids carrying an inducible promoterfor the overexpression of the Omp fusion protein. A vector may includeone or more selectable markers, as defined herein, one or more cloningsites, for example to allow homologous recombination with native nucleicacid, one or more regulatory elements as defined herein, and one or moreorigins of replication. Two or more nucleic acid molecules as definedherein may be provided in a single vector, where desired. These may beunder separate regulatory control, or be operably linked to the sameregulatory elements.

A nucleic acid sequence or genetic construct as described herein may beprovided in a host cell for expression of a modified membrane spanningprotein of the invention. Suitable host cells for recombinant proteinexpression include eukaryotic or prokaryotic cells, preferably thelatter. Suitable host cells will be known and available to personsskilled in the art, and include for example E. coli, BL21, BL21 AI, BLR,and Rosetta-2. There may also be provided a host cell comprising agenetic construct as described herein. The host cell may be recombinant.

The present invention provides a method of binding a component in asample, the method comprising:

-   -   i) providing a polymeric substrate comprising a membrane        spanning protein immobilised thereon, wherein the membrane        spanning protein is immobilised upon the substrate by        physisorption, and wherein the membrane spanning protein anchors        a heterologous protein or peptide for display;    -   ii) adding sample to the substrate;    -   iii) maintaining the substrate with sample under conditions to        allow binding of any component to the substrate.

Preferably, after addition of the sample to the substrate, the substratemay be incubated for a suitable period of time to allow any analyte tobind to the substrate. The incubation period may vary depending upon theassay and the sample type, but typically may be from 5 minutes to 24hours, more preferably 10 min to 1 h depending on the assay beingperformed.

The method of the invention may be a screening assay, to detect thepresence of absence of a component of interest in a sample. In such anassay, prior to detection to maximise accuracy of the assay, the methodmay comprise a step of washing the substrate to remove any unboundmaterial. Washing may be performed with any suitable buffer, water, orsolutions containing detergent or ethanol for example TBS, PBS, HEPES,TE, 70% ethanol, Tween, or deionised water, preferably sterile.

Detection of bound component may be performed using any suitable methodin the art, for example using a binding assay with a binding partnerspecific for the analyte. In a typical binding assay, the substrate maybe incubated with a binding partner specific for the analyte (forexample, IgG). Bound analyte may then be detected, either directly forexample if it comprises a signal which can be measured, or indirectly,for example by using a second binding member specific for the firstbinding partner. The second binding partner may be an antibodyconjugated to enzyme or catalyst or other marker such as a fluorescenttag, and detection may be performed by incubation with a substrate andmeasuring the amount of signal produced. Any suitable signal may beused, many examples of which will be known and available to personsskilled in the art. Preferred signals are those that can be detected inthe electromagnetic spectrum, such as chromophores and fluorophores, andenzyme substrate systems such as Horseradish peroxidase/TMB. Others willbe known to persons skilled in the art. In the latter case, a bindingmember specific for the ligand may be bound to an enzyme, whichcatalyses the signal substrate to produce a colorimetric output.Preferred signals are those which employ an amplification system. Enzymelabels which can act on a substrate to produce chromophores are mostpreferred, e.g. Horseradish Peroxidase, alkaline phosphatase, betagalactosidase. Suitable substrates include TMB ABTS, OPD (for HRP), pNPP(for AP) and ONPG (for beta galactosidase). A colourimetric output maybe measured visually, or quantitatively by measuring changes inabsorbance of light. The method may further comprise comparing thesignal generated to a standard chart, to obtain a quantitative value ofamount of analyte based upon the signal.

The sample may be derived from a human or animal body (for examplesaliva, whole blood, plasma, urine, semen, faeces, etc) or may be celllysate or crude extract from a production process.

A component may be any moiety, preferably one which is capable of beingbound by a binding partner. A non-limiting selection of ligands includenucleic acid, antigen, antibody, oligonucleotide, hormone, hapten,hormone receptor, vitamin, steroid, metabolite, aptamer, sugar, peptide,polypeptide, protein, glycoprotein, a cell, organism (such as fungus,bacteria, viruses, protozoa and multicellular parasites), therapeutic ornon-therapeutic drugs, or any combination or fragment thereof.Preferably, the component may be an immunologically active protein orpolypeptide, such as an antigenic polypeptide or protein.

The method may also be used for purification of a component of interestfrom a sample. Such a method may be as described above in relation to ascreening method, where instead of detecting component, any boundcomponent may be eluted from the substrate. Any bound product may beeluted from the substrate using methods known in the art, for examplesalt elution, elution by pH change, elution by competitor binding.

The method may also be used for immobilising a component of interestfrom a sample, for example for further reaction, for example asdescribed herein. For example, the peptide and/or protein may comprisean Fc binding domain (e.g. from protein A, G or L), which may serve toimmobilise components exhibiting an Fc domain (e.g. Fc taggedrecombinant protein). Such immobilisation may have a variety of uses,for example in binding assays, cell culture etc.

The method may comprise immobilising a membrane spanning protein on apolymeric substrate, as described herein. Preferably, the polymericsubstrate comprises a membrane spanning protein immobilised thereon,wherein the membrane spanning protein is immobilised upon the substrateby physisorption, and wherein the membrane spanning protein comprises aheterologous peptide and/or protein. The membrane spanning proteincomprises a head and a foot, the head and foot being spaced apart fromone another by one or more membrane spanning strands. By anchors meansthat the membrane spanning protein may comprise a heterologous peptideand/or protein in a loop at the head of the protein and/or aheterologous peptide and/or protein at an N and/or C terminus at thehead of the protein. By modified to anchor means that the membranespanning protein is engineered to comprise an N and/or C terminus at thehead of the protein, and/or one or more loops at the head of theprotein.

Thus, the membrane spanning protein may:

-   -   i) comprises a heterologous peptide and/or protein in a loop at        the head of the protein;    -   ii) comprises a heterologous peptide and/or protein at an N        and/or C terminus at the head of the protein;    -   iii) is engineered to comprise an N and/or C terminus at the        head of the protein; and/or    -   iv) is engineered to comprise one or more loops at the head of        the protein.

A heterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display.

The present invention also provides a method of mediating an interactionof an anchored peptide and/or protein with a component in a sample, themethod comprising:

-   -   i) providing a polymeric substrate comprising a membrane        spanning protein immobilised thereon, wherein the membrane        spanning protein is immobilised upon the substrate by        physisorption, and wherein the membrane spanning protein anchors        a heterologous protein or peptide for display;    -   ii) adding sample comprising a component to the substrate;    -   iii) maintaining the substrate with sample under conditions to        allow interaction of the component with anchored peptide and/or        protein.

Preferably, the method comprises providing a polymeric substratecomprising a membrane spanning protein immobilised thereon, as describedherein.

The sample may be derived from a human or animal body (for examplesaliva, whole blood, plasma, urine, semen, faeces, etc) or may be celllysate or crude extract from a production process, or may be a cellculture of reaction mixture.

A component may be one which is capable of interacting with an anchoredpeptide or protein. It may be any moiety, including for example nucleicacid, antigen, antibody, oligonucleotide, hormone, hapten, hormonereceptor, vitamin, steroid, metabolite, aptamer, sugar, peptide,polypeptide, protein, glycoprotein, cell, organism (such as fungus,bacteria, viruses, protozoa and multicellular parasites), therapeutic ornon-therapeutic drugs, or any combination or fragment thereof. Thecomponent may be an immunologically active protein or polypeptide, suchas an antigenic polypeptide or protein. Preferably, the component is acell. A cell may be a prokaryotic cell, for example a fungal orbacterial cell, or a eukaryotic cell, for example a mammalian cell,preferably a human cell.

Preferably, after addition of the sample to the substrate, the substratemay be incubated for a suitable period of time to allow any reaction ofthe peptide and/or protein with a component of the sample. Theincubation period may vary depending upon the assay and the sample type,but typically may be from 5 minutes to 24 hours, more preferably 10 minto 1 h depending on the assay being performed.

Where the component is a cell, the assay may be useful in providingcellular interactions to a cell culture, for example for exampleproviding peptide or proteins which signal the cell to grow, dividean/or differentiate, or to express a particular characteristic orfunction. For example, the protein may be a growth factor whichinteracts with receptors on the cell surface when the substrate isincubated with cell culture. Alternatively, the peptide may comprise anECM motif, which again may interact with receptors on the cell surface,prompting particular cellular characteristics or differentiation.Examples of modified OMP proteins for use in cell binding assays includeOMP153, 154, 162-165, 167, 174-179, and 180-192 (Tables 3 and 4).

Methods for promoting cell growth and/or differentiation using surfacecoated substrates and methods of cell culture are known in the art, andtheir teaching can readily be applied to using the substrates of thepresent invention in a method of cell culture of promoting cell growthand/or differentiation (see for example Helgason and Miller (Eds.)(2004)Basic cell culture protocols, Humana Press, ISBN 1588292843).

A cell for use in a method of the invention may be a eukaryotic orprokaryotic cell. The cell may be an insect cell, yeast, bacteria, plantcell, algae, and animal cell, preferably mammalian cells. It may be acell line. Animal and mammalian cells fibroblasts, stem cells, inducedpluripotent stem cells, neuronal cells, hepatocytes, myocytes,haematopoietic cells, epithelial cells, primary cells, transformed celllines.

The method may also be useful in an enzymatic assay, for example wherethe peptide and/or protein encodes an enzyme or catalyst. Uponincubation with the sample, the anchored enzyme or catalyst reacts withcomponent in the sample to provide a reaction product. The method maycomprise removing the sample from the substrate and purifying anyreaction product therefrom, or detecting the presence of reactionproduct.

The method may be used for immobilising peptides or proteins which arerequired in an assay, for example a cell culture assay. As describedabove, for example, the peptide and/or protein may comprise an Fcbinding domain (e.g. from protein A, G or L), which may serve toimmobilise components exhibiting an Fc domain (e.g. Fc taggedrecombinant protein). Such immobilisation may have a variety of uses,for example in binding assays, cell culture etc.

The present invention also provides an incubation comprising a polymericsubstrate, a membrane spanning protein, and detergent at a concentrationof 1×CMC or below. Preferably, the membrane spanning protein, substrateand detergent are as described herein. The incubation reflects anintermediate in the manufacture of a polymeric substrate or product ofthe invention, in which a polymeric substrate is incubated with amembrane spanning protein as defined herein, where the detergentconcentration in the incubation is 1×CMC or below. The polymericsubstrate may be unbound or partially bound with membrane spanningprotein which becomes immobilised thereon.

In a ninth aspect of the present invention, there is provided a kitcomprising a polymeric substrate, and a membrane spanning protein whichanchors, or is modified to anchor, a heterologous protein or peptide fordisplay. The membrane spanning protein comprises a head and a foot, thehead and foot being spaced apart from one another by one or moremembrane spanning strands. By anchors means that the membrane spanningprotein may comprise a heterologous peptide and/or protein in a loop atthe head of the protein and/or a heterologous peptide and/or protein atan N and/or C terminus at the head of the protein. By modified to anchormeans that the membrane spanning protein is engineered to comprise an Nand/or C terminus at the head of the protein, and/or one or more loopsat the head of the protein. Thus, there may be provided a polymericsubstrate comprising a membrane spanning protein immobilised thereon,wherein the membrane spanning protein is immobilised upon the substrateby physisorption, and wherein the membrane spanning protein:

-   -   i) comprises a heterologous peptide and/or protein in a loop at        the head of the protein;    -   ii) comprises a heterologous peptide and/or protein at an N        and/or C terminus at the head of the protein;    -   iii) is engineered to comprise an N and/or C terminus at the        head of the protein; and/or    -   iv) is engineered to comprise one or more loops at the head of        the protein.

A heterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display.

The kit may additionally comprise a chart providing dilution factors toenable physisorption of a membrane spanning protein to a polymericsubstrate, diluents, buffers, substrate, immunoglobulin and bindingreagents. The kit may be packaged, for supply and transport. Thecomponents of a kit may be individually packaged and supplied as acombination of reagents to practice a method of the invention.

The methods of the invention may further comprise the step of modifyinga membrane spanning protein, as described herein, prior toimmobilisation of a protein onto a polymeric substrate.

The methods of the invention may further comprise the step of modifyinga nucleic acid sequence encoding a membrane spanning protein, to providea modified membrane spanning protein as described herein, and expressingthe protein from a host cell, prior to immobilisation of the modifiedmembrane spanning protein onto a plastic substrate.

The present invention also provides a product comprising a polymericsubstrate comprising a membrane spanning protein which anchors, or ismodified to anchor, a heterologous protein or peptide for display. Themembrane spanning protein comprises a head and a foot, the head and footbeing spaced apart from one another by one or more membrane spanningstrands. By anchors means that the membrane spanning protein maycomprise a heterologous peptide and/or protein in a loop at the head ofthe protein and/or a heterologous peptide and/or protein at an N and/orC terminus at the head of the protein. By modified to anchor means thatthe membrane spanning protein is engineered to comprise an N and/or Cterminus at the head of the protein, and/or one or more loops at thehead of the protein. Thus, there may be provided a polymeric substratecomprising a membrane spanning protein immobilised thereon, wherein themembrane spanning protein is immobilised upon the substrate byphysisorption, and wherein the membrane spanning protein:

-   -   i) comprises a heterologous peptide and/or protein in a loop at        the head of the protein;    -   ii) comprises a heterologous peptide and/or protein at an N        and/or C terminus at the head of the protein;    -   iii) is engineered to comprise an N and/or C terminus at the        head of the protein; and/or    -   iv) is engineered to comprise one or more loops at the head of        the protein.

A heterologous peptide and/or protein may be provided at an engineered Nand/or C terminus at the head of the protein, or in an engineered loopat the head of the protein, for display.

A product may include micro-well plates, tissue culture flasks orplates, plastic beads, fibres, mesh substrates, medical devices such assurgical implants, micro- or nano-particles of polymers. There isprovided a surgical implant comprising a polymeric substrate comprisinga membrane spanning protein immobilised thereon, wherein the membranespanning protein is immobilised upon the substrate by physisorption, andwherein the protein retains its native secondary structure.

Examples

In order to investigate the binding and function of our β-barrel basedproteins to polymers the following approaches have been adopted:

1. Immunoassay for Detection of Protein on Polymers

Comparison of OMP18 (two IgG-binding B domains of SPA fused to OmpA) andnative Staphylococcus aureus Protein A (five IgG-binding domains).

Detection of FLAG-tagged OMP proteins on various polymers Detection ofhuman HIV p24 antigen fused to OMP scaffold with specific antibody andcomparison to native antigen

2. Cell Culture

Comparison of cell attachment to OMP0 scaffold protein and variousconstructions containing ECM protein motifs or growth factors displayedon the OMP scaffold.

Binding of IgG to Native Protein a or Protein a Domains Anchored withβeta-Barreled Scaffold

For any scaffold to be effective as an anchor for a second independentprotein, it must improve the function of that protein when adsorbed to asurface. To examine this for the beta-barreled scaffold, experimentswere performed using one of the range of IgG-binding proteins OMP18,which has a tandem repeat of the IgG-binding B-domain of Staphylococcusaureus Protein A fused to the N-terminus of the OMP9 scaffold. OMP9 isshown in FIG. 1, and is a gold binding beta barreled protein comprisingall extracellular loops, cysteine residue for gold binding, circularlypermutated N and C termini and a shorted N terminus, which in OMP18 isfused to the tandem repeat of the IgG-binding B-domain of Staphylococcusaureus Protein A. This latter domain binds to the Fc region of antibodyleaving the antigen-binding regions exposed.

OMP18 can capture IgG antibodies on a gold biosensor surface withgreater efficiency than adsorbed or amine coupled protein A (unpublisheddata). In order to test whether this would be the case for Protein Adomains tethered to plastic via the OMP scaffold, a comparison ofimmobilisation of OMP18 vs Protein A on polystyrene surfaces in the typeof immunoassay described in FIG. 4 was conducted. In this scenario, itwas envisaged that correctly oriented proteins would bind larger amountof antibody than incorrectly oriented or denatured proteins, therebyyielding an improved signal from the immune-detection.

Protein Adsorption of OMP18 and Protein A to Plastic Well Plates

One hydrophobic 24-well plate (Corning) and one ‘hydrophilic’ plate(Corning) were used. OMP18 (Lot 15910BE16511LH) was in PBS (phosphatebuffered saline)+0.25% OG (n-octylglucoside) at 70 μg/mL (2 μM) andnative Staphylococcus aureus Protein A (Sigma Cat. No. P7387; Lot055K09261) in PBS+0.25% OG at 84 μg/mL (2 μM). 300 μL of proteinsolution was applied to wells on both plates. Blank wells (no protein)were prepared with just PBS+0.25% OG. The plates were incubatedovernight on rocking platform (rocker) at room temperature (RT). Wellswere coated in triplicate with each protein.

Immunoassay to Compare OMP18 with Native Protein a on Plastic

The wells were washed once with Tris-buffered saline+0.05% (v/v) Tween20 (herein referred to as TBS-T). Note, all washes and incubations werewith 300 μL of solution unless stated otherwise. Mouse IgG (Sigma CatNo. 15381, Lot. 025K7580) at 2 μg/mL in Tris-buffered saline+0.05% (v/v)Tween 20+3% (w/v) BSA (herein referred to as TBS-TB) was added to twowells of each type and TBS-T was added to a no antibody control well andincubated for 1 h at RT on rocker. Mouse IgG solution and TBS-T solutionwere removed and wells washed three times with TBS-T. Rabbit anti-mouseIgG-AP conjugate (Sigma Cat. No. A3688, Lot. 103K9157) diluted 1/5000 inTBS-T was added to all the wells. The wells were maintained for 1 h atroom temperature on a rocker. Conjugate was removed and the wells washedin 3×TBS-T. 200 μL of (PNPP) substrate was added to each well andincubated 30 min room temperature in dark. The reaction was stopped bythe addition of 50 μL of 3M NaOH solution in deionised water. Thecontents of the well were mixed with 0.75 mL of deionised water andabsorbance at 405 nm was measured in a Shimadzu 1240 spectrophotometer.

The raw data is in Table 1 and plotted in FIG. 5 as a bar graph.

TABLE 1 A₄₀₅ readings from each well. No Protein No Protein OMP18 OMP18Protein A Protein A Hydrophilic Hydrophobic Hydrophilic HydrophobicHydrophilic Hydrophobic mIgG 0.018 0.001 2.237 2.390 1.258 0.014 Well1mIgG 0.019 0.005 2.233 2.332 1.433 0.010 Well 2 No IgG 0.023 0.005 0.0270.056 0.025 0.003 Conjugate only

Use of Flag-Tagged OMP Scaffolds on PLA

As a hydrophobic polymer, polylactic acid (PLA) was considered to be agood candidate as material to which OMP proteins could be attached. Inorder to assess this, some 3D printed PLA discs were obtained from Prof.K Dalgarno (Newcastle University). The structure of the discs is shownin FIG. 6.

Protein Adsorption onto PLA Discs

A hydrophobic 48 well plate (Nunc) was used to hold the discs duringtreatment. OMP0 (Modified OmpA protein comprising a cysteine residue atposition 10 to enable gold binding (see FIG. 13 for the sequence ofOmp0).) (Lot. 91012BE12313) and OMP5 (Lot. 8910BE18213) were diluted to32 μM in PBS containing diluted detergent as before. 600 μL were addedto each PLA disc, control discs were treated with the same solutionlacking protein. The 48 well plate was sealed with parafilm and storedat 4° C. for 16 hours. Each PLA disc was washed twice with sterilized500 μL deionized water (Lot. 251013YD) to remove excess unattachedprotein. OMP5 is the OmpA with a FLAG epitope in extracellular loop 1.The FLAG epitope is DYKDDDDK.

Antibody Detection of OMP5

A 1:1000 dilution of M2 anti-FLAG alkaline phosphatase conjugatedantibody (Sigma Cat No. A9469; Lot. 091 M6287) was prepared in TBS-T.Treated PLA discs were transferred to a new 48 well plate (Nunc) and 500μL diluted antibody was added to each PLA disc. After 30 minutes at roomtemperature the antibody solution was removed and each disc wasincubated twice for 5 minutes in 500 μL TBS-T. 500 μL 1 Step PNPPreagent (Sigma Cat No.; Lot. NI14473612) was added to each PLA discafter 5 minutes at room temperature the reaction was stopped by theaddition of 500 μL 1M NaOH (Lot.). 200 μL solution was removed from eachwell containing a PLA disc and transferred to a 96 well plate. Theabsorbance of the wells was measured at 405 nm using a Thermo ScientificMultiskan FC microplate reader.

The raw data is in Table 2 and plotted in FIG. 7 as a bar graph.

TABLE 2 Absorbance at 405 nm for each well. Blank OmpA OMP 5 0.412 0.3120.88 0.335 0.361 1.086 0.369 0.374 0.877

Use of OMP Scaffolds to Display ECM Motifs on Polyester Fibres andPolystyrene Plates

It has previously shown that OMP's modified OmpA proteins assembled asan oriented monolayer on gold⁷ and that the addition of integrin bindingmotifs to the β-barrel could improve the attachment of cells to goldsurfaces⁹. In the experiments detailed here it was examined whetherbinding of these proteins to polyester fibres improved the attachment ofcells.

Use of OMP Proteins with Discs Made from Electrospun Polyester Fibres

Discs made from electrospun polypropylene fibres with a polyethylenecore were sourced from Applied Cell Biotechnologies Inc. and were coatedwith OMP36 using dialysis to remove the detergent from the proteinsolution. OMP36 contains the YIGSR motif from laminin. Once treated withprotein the fibre discs were seeded with cells and the number of cellsattached was assessed by microscopy.

Protein Treating Polymer Fibres.

Electrospun polymer samples were placed in Spectra/Por rc dispodialyser(15000 Dalton molecular weight cut off; Lot. 3205922) with 5 mL OMP36(Lot. 22605BE23407) at 10 μg/mL in ROG-8 buffer, duplicate samples weretreated with protein-free ROG-8. The dialysis bags were placed in a 1litre beaker containing 800 mL dialysis buffer (50 mM Tris, 0.1 mMEDTA), a magnetic stirrer was used to gently stir the solution. Thedialysis buffer was removed and replaced with fresh buffer at 2 hours,30 hours, 38 hours and 4 days. After 5 days the polymer samples wereremoved from the dialysis tubing and were washed deionized water.

Testing Electrospun Polymer Fibres with Cells

Polymer discs were soaked in 70% ethanol for 10 minutes to sterilizethem prior to addition of the cells; this was followed by a quick washin PBS (Lot. 15307SP) to remove any residual ethanol. PC12 neuronalcells (passage 27, ˜90% confluent) were harvested with trypsin/EDTA andsuspended in RPMI1640 media (containing 10% Foetal calf serum) at 1×10⁶cells per mL.

3 ml of cells were added to duplicate OMP36 treated and protein-freeROG-8 treated polymer discs. The cells were incubated overnight at 37°C., 5% CO₂ in a humidified incubator. After 16 hours the discs weresoaked in PBS containing 4% w/v paraformaldehyde (BDH; Lot. K32259648)at room temperature for 10 minutes followed by 30 minutes in PBScontaining 1 μg/mL DAPI (Lot. 50307SP). Cells were visualized using afluorescent microscope.

The DAPI staining clearly shows the nuclei of many cells on each fibrousmaterial, but there are many more cells on the OMP36 treated fibres.

Adsorbed OMP Scaffold on Polystyrene Plates with Cells

Above it was shown that the β-barreled molecules were still able toimprove cell attachment even when they were adsorbed onto polyesterfibres. It was then examined whether a similar effect could be achievedon polystyrene tissue culture multi-plates just by drying the proteinsonto the plates.

Protein Treatment of Polystyrene Plates.

6 and 12 well tissue culture modified (hydrophilic) Nunclon Δ plates(Nunc) were incubated with OMP36 in PBS with 0.25% OG as before at 4° C.for 16 hours. 6 well plates contained 500 μL protein per well the 24well plates contained 300 μL protein per well. After incubation eachwell was washed twice with deionized water then sprayed with 70% ethanolto sterilize. The plates were left in a cell culture hood for 10 minutesto allow most of the ethanol to evaporate then each well was washed withsterile PBS.

Testing Protein Treated Plates with 3T3 Murine Fibroblasts

3T3 fibroblasts (passage 147 ˜70% confluent) were harvested usingtrypsin/EDTA and resuspended at 5×10⁴ cells per ml Dulbecco's modifiedEagle's medium (containing 10% foetal calf serum). 3 untreated wells and3 protein treated wells in a 6 well plate were each seeded with 3 mLcells. 4 untreated wells and 4 protein treated wells in a 24 well platewere each seeded with 750 μL cells. Plates were incubated overnight at37° C., 5% CO₂ in a humidified cell culture incubator. After 16 hoursincubation the media was discarded from each plate and PBS containing 4%w/v paraformaldehyde (BDH; Lot. K32259648) at room temperature for 30minutes followed by 10 minutes in PBS containing 1 μg/mL DAPI (Lot.50307SP). Cells were visualized using a fluorescent microscope and thenumber of cells in free random fields of vision per well were counted.

Data are plotted in the bar chart shown in FIG. 9. Treating polystyreneplates with OMP36 improves the attachment of cells to the polystyrene.

Use of OMP Scaffolds for the Display of Growth Factors for Cell Culture

The first cell culture experiments targeted enhancing the attachment ofcells to surfaces, as the protein technology was developed to allow theinsertion of larger proteins and peptides into OMP scaffolds we widenedour interest to include much larger targets such as growth factors. Thefirst two growth factors selected as targets for engineering wereFibroblast Growth Factor 1 (FGF1, acidic FGF) and Fibroblast GrowthFactor 2 (FGF2, basic FGF). The work documented here covers experimentsattaching FGF1 and FGF2 to polystyrene plates and testing the effectswith mouse 3T3 fibroblasts.

Protein Treating Polystyrene Plate

500 μL 2 μM protein solutions were prepared in Dulbecco's phosphatebuffered saline (D-PBS sourced from Sigma, Lot. 090512SP) containing0.25% n-octylglucoside; OMP0 (Lot. 230511), OMP90 (FGF1; Lot.170809BE201009) and OMP128 (FGF2; Lot 120111BE170111). 100 μL of eachprotein solution were added to 4 wells of a 96 well polystyrene plate,this was followed with 100 μL D-PBS per well. The 96 well plate waswrapped in parafilm and stored overnight at 4-8° C. After 16 hours theprotein solutions were removed and each well was washed with 100 μL 1%Triton-X-100 in deionised water followed by two 100 μL deionised waterwashes. The 96 well plate was air dried then sealed in plastic andstored at 4-8° C.

Testing FGF Treated Plates with 3T3 Fibroblasts

Murine 3T3 fibroblasts (passage 157, ˜90% confluent) were harvested withtrypsin/EDTA and resuspended in Dulbecco's Modified Eagle's Media (DMEM;containing 10% foetal calf serum) at 1×10⁴ cells per mL. The 12protein-coated wells and 4 untreated wells were each seeded with 200 μLcell suspension. An additional 4 untreated wells were seeded with 200 μLcell suspension containing 12.5 ng/mL soluble FGF2 (R&D Systems). Platesseeded with cells were incubated at 37° C., 5% CO₂ in a humidifiedincubator for 18 hours. Media containing unattached cells was discarded,100 μl D-PBS containing 4% w/v paraformaldehyde (BDH; Lot. K32259648)was added to each well, after 30 minutes at room temperature the D-PBSwas replaced with 100 μL Crystal Violet solution (Pro-Lab Diagnostics;Lot. K12560) after a further 30 minute incubation the staining solutionwas discarded and each well was washed 3 times with 100 μL deionisedwater. The wells seeded with cells were examined using an invertedmicroscope, 1 random field of vision was selected per well and all thevisible cells were counted.

Data are shown below in FIG. 10. Both OMP90 (FGF1) and OMP128 (FGF2)replicate the mitogenic effect observed when culturing the fibroblastsin the presence of 12.5 ng/mL soluble FGF2. Treating the polystyrenewells with OMP0 (OmpA scaffold) has no effect on the number of cellsobserved after 24 hours. The mitogenic effects of OMP90 and 128 aresimilar when the proteins are self-assembled as an oriented proteinmonolayer on a gold coated glass coverslip.

Engineered Variants of the Beta-Barrel Protein Scaffold

Leckband, D. and Langer, R. (1991) describe an approach for the stableimmobilization of proteins. Biotechnol Bioeng 37: 227-237. The workdescribed here has been carried out with derivatives of the E. coli OmpAprotein.

Construction of Expression Clones

In each case the novel sequence of amino acids was back-translated toDNA sequence and codon optimized for expression in E. coli. The DNAfragments were synthesized as cassettes or whole genes by an externalcontactor Integrated DNA Technologies (IDT) under confidence and withoutany knowledge of the purpose or function of the novel genes. More detailabout each base scaffold type is provided below (2.5.3. onwards)

The molecular construction of expression clones for the novelmodifications of the β-barrel proteins was carried out using standardmolecular biology techniques that are described in detail elsewhere(Sambrook, J. and Russell, D. W. (2001) Molecular cloning. A LaboratoryManual. CSHL Press). Correct constructs were identified initially byrestriction analysis and validated by DNA sequencing carried out byexternal contractor Beckman Coulter Genomics under confidence andwithout any knowledge of the purpose or function of the sequence. Thenovel β-barrel proteins were used as scaffolds for the fusion of otherproteins and peptides of interest for immobilization on plastics asdescribed in the sections below.

OMP170-Type Scaffolds Fused to HIV P24 Antigen

In order to exemplify the significant advantages of the technology wecreated variants of the OMP170-type β-barrel proteins fused to the HIVp24 protein and demonstrated markedly improved recognition byantibodies. The experiments are recorded in Book 55. OMP170 and OMP171are two scaffold proteins with truncated loops and truncated C-terminus.They also have the cysteine left intact so that the proteins can be usedon both gold and plastic. OMP170 has, in addition, an alpha helicalspacer at the N-terminus that separates the fusion site from theβ-barrel—this separates the domains and allows more efficient refolding.The alpha helical spacer is a mutated form of the Staphylococcus aureusProtein A B domain that does not bind to IgG. The construction is basedupon the mutated version of the D domain that was reported by Kim et alKim, H. K. (2010) Nontoxigenic Protein A vaccine formethicillin-resistant Staphylococcus aureus infections in mice. J ExpMedicine 207: 1863-1870. An alignment of OMP171 with OMP59, which isOMP9 with an alpha-helical spacer, is shown in FIG. 11.

Construction and Purification of Fusion Proteins

Novel recombinant fusion proteins with human HIV P24 protein consensussequence derived from major subtypes (C, B, A, D, F, G, H, J, K,CRF01_AG and CRF03_AB) was fused to the OMP171 scaffold protein (FIG.12). The coding sequence for the P24 consensus for fusion to the OMPscaffold was generated by backtranslating the amino acid sequence andcodon optimization for expression in E. coli. This was ligated with thescaffold coding sequences using standard molecular biology techniques(Sambrook, supra) The native P24 was recombinant HIV P24 antigenpurchased from Capricorn Inc (Cat No. HIV-007-B0646, Lot. HIV130759).OMP171 and 173 were purified and refolded from inclusion bodies asdescribed below (see General Methods below).

Immobilisation on Plastic Plates

Native P24 was diluted to 4 μg/mL in PBS buffer. OMP171 and 173 werediluted to 2 μM in PBS containing 0.25% (w/v) OG. 200 μL of dilutedproteins were added to wells of 96-well untreated polystyrene plates(Corning #3370) and also to Polysorp plates (Nunc #475094). The proteinswere allowed to bind overnight at 4° C. and then washed three times with200 μL of autoclaved deionised water (SDVV) and used immediately.

Detection with Anti-P24 Antibodies

Two types of monoclonal anti-P24 antibodies were purchased fromCapricorn: 1. Anti-HIV1-P24 monoclonal antibody from mouse (Cat No.HIV-018-48294, Lot. HIV122936); 2. Anti-HIV1/2 P24 monoclonal antibodyfrom mouse (Cat No. HIV-018-48304, Lot. HIV111641).

1. The wells were blocked with TBS-TB. 30 min room temperature.2. The two antibodies were each diluted to final concentrations of 0.5,1, 10, 50, 100, 500 and 1000 ng/mL in TBS-TB. 200 μL of eachconcentration were added to three wells of each type of antigen surface.Zero control was carried out on each surface by the addition of TBS-TBalone. 30 min room temperature.3. The wells were washed thrice with 200 μL of TBS-T.4. 200 μL of 1/10000 dilution of secondary antibody, goat anti-mouse IgGalkaline phosphatase conjugate (Sigma Cat. No. A3688, Lot. 103K9157) inTBS-TB were added to each well. 30 min room temperature.5. The wells were washed thrice with 200 μL of TBS-T.6. 100 μL of p-nitrophenyl phosphate liquid substrate (Sigma) were addedto each well. 15 min at room temperature.7. Reaction stopped by addition of 50 μL of 3M NaOH to each well.8. A₄₀₅ measured using a plate reader.

The data plots are shown in FIG. 13. The native P24 antigen that wasdirectly adsorbed to the surfaces was not recognized at all by eitherantibody on polystyrene plates. On the Polysorp plates, the native P24showed signal with both antibodies but that with Anti-HIV1-P24monoclonal was quite poor compared with Anti-HIV1/2 P24. The P24 proteinpresented as a fusion with β-barrel scaffold gave excellent results onboth types of plates with both antibodies. The results were much betterthan expected compared to the native P24 and there was no non-specificbinding to the scaffold by itself (OMP171). These data indicate that theP24 bound to the surface via the β-barrel scaffold anchor is highlyfunctional for antibody recognition compared to native P24, most likelyowing to presentation of the correct structure in an active, accessibleorientation. The beneficial effect is much greater than we expected orthought possible. Thus the β-barrel scaffold technology fulfils thecritical requirements of retention of function of the fusion partnerwhen immobilized on the surface and improves significantly on currentstate-of-the art techniques.

Modified β-Barrel Scaffold for the Display of Small Peptide Motifs

The display of small peptide motifs of 3-50 amino acids presents adifferent challenge compared to larger proteins. They may not beelevated enough from the surface and might remain hidden andinaccessible among the bulk protein. This is a disadvantage since one ofthe main applications for small motif display is in cell culture wherethe motif needs to be exposed enough to interact with components of thecell envelope.

To this end we have designed a scaffold backbone that allows theinsertion of small motifs on an elongated loop with hydrophilic aminoacids and a semi-rigid PT linker (OMP154-type). The PT linker is anaturally occurring amino acid sequence (Poon, D. K. Y. et al. (2006)Direct Demonstration of the Flexibility of the GlycosylatedProline-Threonine Linker in the Cellulomonas fimi Xylanase Cex throughNMR Spectroscopic Analysis, J Biol Chem 282: 2091-2011)

Construction and Purification of Fusion Proteins

The OMP0 scaffold protein was modified to remove three of the fourextracellular loops, the basic modified scaffold was named OMP154. Thedifferences between OMP0 and OMP154 shown in the alignment of FIG. 14.

The gene encoding OMP154 was synthesized at IDT and cloned and verifiedusing standard molecular biology procedures (Sambrook, supra) andpurified using our standard methods (see General Methods below).

Once the OMP154 backbone scaffold protein was completed, variousinsertions were made into it as shown in Table 3.

TABLE 3 List of new proteins with motifs displayed in the long loop ofOMP154 Protein Name Insertion details OMP153 154 with RGDS in long loopOMP162 154 with IKVAV from laminin α1 in long loop OMP163 154 with YIGSRfrom laminin β1 in long loop OMP164 154 with 2xPHSRN in long loop OMP165154 with Collagen IV- MNYYSNS in long loop OMP174 154 with two FHRRIKAmotifs from collagen in tandem in long loop OMP175 154 withIPKASSVPTELSAISMLYLDENEKVVLK from human BMP2 protein in long loop OMP176154 with PQVTRGDVFTMP from human vitronectin in long loop OMP177 154with KKQRFRHRNRKGYSRQ from human vitronectin in long loop OMP178 154with VDTYDGRGDSVVYGLRSKSKKFRR from human osteopontin in long loop OMP179154 with VFDNFVLK motif from human Tenascin-C in long loop OMP185 154with Collagen I GTPGPQGIAGQRVV motif in long loop OMP186 154 with HivTAT SYGRKKRRQRRRAHQ motif in long loop OMP187 154 with VQLRNGFPYFSY fromlaminin α2 in long loop OMP188 154 with GLLFYMARINHA from laminin α2 inlong loop OMP189 154 with IKVSV from laminin α2 in long loop

These proteins were created either by gene synthesis of the completecoding sequence or by insertion of small double stranded oligonucleotidecassettes encoding the motif of interest into the cloning site in themiddle of the loop in pOMP154 expression plasmid using standard methods(Sambrook, supra). The proteins were expressed and purified as describedin section entitled General Methods below.

Immobilisation of Small Peptide Motifs on Polystyrene

Protein at 1 μM was prepared in PBS containing dilute detergent solutionas before. This was added to each well of a well plate as before. After16 hours each well was washed twice with sterilized 200 μL deionizedwater to remove excess unattached protein.

Culture of MG63 Cells on Small Peptide Motif Treated Plates

The protein treated 96 well plate was sprayed with 70% ethanol and leftin a cell culture for 10 minutes for the ethanol to evaporate. Each wellwas then washed with D-PBS to remove any unevaporated ethanol. MG63osteosarcoma cells (passage 5) were grown until ˜80% confluent beforethey were harvested with trypsin/EDTA. Cells were resuspended in DMEM(containing 10% foetal calf serum) at 1×10⁴ cells per mL.

100 μL cell suspension was added to each well of the 96 well plate, theplate was then incubated for 16 hours at 37° C., 5% CO₂ in a humidifiedcell culture incubator.

Quantification of Cells Cultured on Small Peptide Motif Treated Plate.

A PNPP assay was used to provide semi-quantitative assessment of thenumber of attached cells in each well using the intracellular acidphosphatases to create a colour change in the PNPP reagent. PNPP reagentwas prepared by dissolving 1 mg per ml PNPP (Sigma Lot. SLBC5466V) inPNPP reagent buffer (0.1M Sodium acetate pH5+0.1% Triton X-100; Lot.220113SP). The cell media was removed from all the wells, 100 μL PNPPreagent was added to each well, the 96 well plate was wrapped inaluminium foil and incubated at 37° C. for 2 hours. The reaction wasstopped by the addition of 10 μL 1M NaOH (Lot. 021111DS) to each well.After gentle shaking 85 μL was transferred from each well to a new 96well plate and the absorbance at 405 nM was measured using a ThermoFisher Multiskan FC plate reader.

The results are in line with what we would predict with a wide range ofeffects from the different proteins, OMP154 improves cell attachmentcompared to the blank well by reducing the hydrophobicity of the surfaceand thus making it easier for the cells to attach. A similar level ofimprovement is seen with a large percentage of the tested proteins.

MG63 cells show enhanced cell attachment, compared to OMP154, when grownon the surfaces OMP153, 177 and 178. OMP153 displays the RGDS motiffound in fibronectin, vitronectin, osteopontin, etc and is a verypowerful integrin binding motif that interacts with many different celltypes. OMP177 and 178 both display vitronectin motifs, an ECM componentfound in mineralised bone. The results clearly show that the OMP154based proteins display their engineered motifs in such a way that theyare accessible for cells to interact with. With several of the testedproteins significantly enhancing the attachment of the osteosarcoma cellline MG63.

OMP140-Type Scaffolds Fused to Growth Factors

In order to exemplify the significant advantages of the technology forthe presentation of immobilized growth factors on tissue culture plates,we created variants of the OMP140-type β-barrel proteins fused tovarious growth factor as listed in Table 4. ORL140 is a scaffold proteinwith truncated extracellular loops and truncated C-terminus. It has thehis tag at the C-terminus which ensures that only full length expressedproteins carry the his tag and can be purified by metal affinitychromatography. This allows the fusion of large proteins such as growthfactors and alleviates concerns about premature translational stops thatcan occur when overexpressing large proteins. It also has the cysteineresidue removed. Most growth factors have numerous internal disulphidebridges that are essential for the maintenance of structure andfunction; cysteine present in the scaffold could interfere with theformation of these specific disulphide bridges and the cysteine-freevariant of the scaffold alleviates this problem.

Note that apart from the C-terminal His-tag, the lack of cysteineresidue, and the lack of the C-terminal NQ residues, OMP140 is identicalto OMP171 (see FIG. 9)

Construction and Purification of Fusion Proteins

The OMP140 coding sequence was synthesized by IDT and cloned into theexpression vectors using standard methods (samboork, supra). A series ofnovel fusion proteins with OMP140 were created by ligating syntheticcassettes (designed at OMP and codon optimised for E. coli) coding forgrowth factors into the pOMP140 such that they were at the N-terminus ofthe fusion proteins. A list of constructs created to date is shown inTable 4.

TABLE 4 Fusions of growth factors to OMP140 Protein Name Insertiondetails pOMP167 Human epidermal growth factor in OMP140 pOMP180 HumanLeukaemia Inhibitory Factor (LIF). Amino acids 23 to 20 of P15081 inUniProt. Isoform 1. fused to N-terminus of OMP140 pOMP181 Humanfibroblast growth factor 4 (FGF-4). Amino acids 31-206 of P08620 inUniProt. Isoform 1. fused to N-terminus of OMP140 pOMP182 HumanInterleukin-4 (IL-4). Amino acids 25-153 of P05112, Isoform 1. fused toN-terminus of OMP140 pOMP183 Human stem cell factor (SCF). Amino acids26-190 of P21583 (also known as ‘Soluble Kit ligand’ fused to N-terminusof OMP140 pOMP184 Human Sonic Hedge Hog (Shh). Amino acids 24-197 ofQ15465 fused to N-terminus of OMP140 pOMP190 Human granular macrophagecolony stimulating factor (GM-CSF). Amino acids 18-144 of P04141 fusedto N-terminus of OMP140 pOMP191 Human interleukin 3 (IL-3). Amino acids20-152 of P08700 fused to N-terminus of OMP140 pOMP192 HumanThrombopoeitin (TPO). Amino acids 23-195 of P40225 fused to N-terminusof OMP140

The proteins were expressed and purified as described in Section 3.1 butthe refolding conditions for them varied: The standard refolding bufferwas supplemented with 1 mM DTT and 0.4 M arginine.

General Methods Protein Purification and Refolding

OMP proteins were expressed as inclusion bodies in E. coli BL21 strainby IPTG induction in 1 litre of LB selective medium. The cells werelysed in BugBuster solution (Novagen) and inclusion bodies enrichedusing the wash protocols in the Instruction Manual for BugBuster.

Inclusion bodies were solubilised in HTBB buffer (20 mM NaPO₄, 0.5 MNaCl, 20 mM Imidazole, 8 M Urea pH7.4, filtered and degassed). Thesolubilised preparations were purified by immobilized metal affinitychromatography on HisTrap HP columns (GE Healthcare) on an AKTAPrimesystem with fraction collector using a pre-programmedbinding-wash-elution method—the elution was a step elution in HTBB+250mM Imidazole.

The peak fractions from the elution were collected and purity determinedby SDS PAGE. Fractions deemed to be >95% homogenous for the protein ofinterest were pooled and concentrated using a Vivaspin centrifugalconcentrator to volume of <1 mL. The purified protein was refolded bydilution (by a factor of at least 1 in 10) into refolding buffer (50 mMEthanolamine, 0.1 mM EDTA, 1% OG, 1 mM DTT).

The extent of refolding was estimated by bandshift on SDS PAGE andfurther verification carried out where necessary by circular dichroismspectroscopy and functional assays (not shown here).

SDS Page

The NuPAGE SDS PAGE gels, buffers and stains from Invitrogen were usedaccording to manufacturer's instruction.

Effect of Detergent on Binding of OMP18

In order to test the effect of detergent we looked at some commonly useddetergents in biology for their suitability in allowing OMPprotein tobind to polystyrene surfaces.

Table 5 below lists the detergents and their properties.

Critical Micelle Detergent MW Concentration (CMC) n-octyl glucoside (OG)292 20-25 mM n-dodecylmaltoside (DM) 511  0.15 mMNonaethyleneglycolmonododecylether 583  0.1 mM (Thesit, Polidocanol)

In order to gain a realistic comparison of detergents we used the CMC asthe factor to determine concentration for example OG at 22.5 mM wasdefined as 1×CMC or DM at 0.3 mM was defined as 2×CMC etc.

In the first experiment all three detergents were used at variousconcentrations around the CMC to immobilize OMP18 for 6 or 24 h andcarried out the immunodetection as above. OMP18 protein at 1 μMconcentration was prepared in PBS containing 2×CMC of detergent. Thiswas added to wells of a 96-well plate in a series of dilutions to give2×, 1×, 0.5× and 0.25×CMC for each detergent.

One set of wells was washed and processed after 6 hours and a second setwas incubated for 24 hours. Following washing a drying, the immunoassaywas carried out as described above but with a single mouse IgGconcentration at 1 μg/mL.

The data is shown graphically in FIG. 22.

At high detergent concentration at CMC or above there is little bindingof protein to the surface as indicated by the low signal from theimmunoassay. In all cases precipitation was not observed at the lowestdetergent concentration.

In each case the 6-24 h incubation with Orla protein gave the optimumresult.

Effect of OMP18 Concentration

This experiment aimed to determine the effect of OMP18 concentration onsurface performance. It may be useful to limit the amount of protein onthe surface for certain applications and the ability to control thesurface density would be desirable.

OMP18 was diluted at different concentrations in detergents at 0.125×CMCin PBS buffer in wells of a 96 well untreated polystyrene plate. Eachwell had 200 μL of solution and the plate was incubated at 4° C.overnight. After washing and drying the immunodetection was carried outas above with mouse IgG at 1 μg/mL.

The data are shown graphically in FIG. 23.

The data show that the surfaces are close to saturation with theaddition of protein at 100 nM and that it is possible to control thecoverage by varying the protein concentration (and the detergentconcentration as shown above).

Pattern Spotting on Surfaces

It would be useful to create patterns of protein on surfaces fornumerous applications such as arraying, cell culture, drug discovery,and so on. The method described herein should be amenable to printingand patterning.

10 μL spots of OMP9 (control protein) and OMP18 (IgG-binding domains onOMP9 scaffold) were pipetted onto the bottom of 6 well polystyreneplates and adsorbed overnight on a humidity chamber at RT (the spots didnot dry overnight under these conditions).

The proteins were at a final concentration of 5 μM in detergent at0.4×CMC in each spot.

The wells were washed 2×2 mL TBS-T and once with water and dried.

Blocked with 2 mL TBS-T+3% BSA for 1 h.

Then 1 mL of mouse IgG at 0, 0.1 or 1 μg/mL in TBS-T+3% BSA was added toeach well and incubated for 15 min.

After 3×2 mL washes with TBS-T, 1 mL of anti-mouse IgG-AP conjugate1/10000 dilution was added and incubated at RT for 15 min.

The wells were washed 3×2 mL TBS-T and once with water.

BCIP/NBT substrate was added (0.5 mL) and incubated for 15 min at RT.

Reaction was stopped by washing 3×2 mL water and the wells were dried.

A scan of the plate is shown in FIG. 25. The dark shadows indicate areaswhere protein was bound. These correspond to where the spots wereplaced.

In this case, the 10 μL of solution spread out into spots with anaverage diameter of 5.5 mm. This spot size would be good for cellculture applications. It should be possible to create smaller spots byusing lower volume of protein at higher concentration. Note that thereis normally some cross reactivity of polyclonal antibodies with OMP9.

These data suggest that the method for immobilizing OMP proteins on asurface should be amenable to more precise and sophisticated patterningand lithographic techniques.

Functionalisation of Polystyrene Beads with Omp Proteins

We have demonstrated improved function of OMP proteins on planar plasticsurfaces and it was desirable to test if these advantages andimprovements in function could be reproduced on particles and beads thatare important in many applications such as bioprocessing. In order toexemplify this we coated polystyrene beads with OMP85 protein (Protein Gdomains fused to the Omp scaffold) or Staphylococcal protein A in itsnative form and attempted to purify IgG from human serum using thecoated beads as the capture agent.

Polybeads of 1 μm diameter were obtained from Polysciences Inc. Asuspension of 0.5 g of polybeads was made in 20 mL of PBS+0.01% SDS togive a preparation containing 2.5% solids i.e. 4.55×10¹⁰ particles/mL.The binding of Protein A or OMP85 to the polybeads was carried out in 2mL final volumes of PBS containing 1 mL of 2.5% polybeads, 0.5 mg ofprotein and dodecylmaltoside (DM) at a concentration of 0.125×CMC. Anadditional ‘untreated’ sample was prepared by mixing 1 mL of polybeadsand 1 mL of PBS. All were left overnight at 4° C. after mixingthoroughly. The polybeads were centrifuged and washed 3× by resuspensionin 1 mL of TBS-T and centrifugation. Then each pellet was resuspended in0.5 mL of TBST and 0.5 mL of human serum were added and incubated for 10min at RT. The polybeads were centrifuged and the pellets washed 4×1 mLTBS-T. Supernatants were saved for analysis on SDS PAGE. Bound IgG waseluted by resuspension of the washed pellets in 1 mL 50 mM Na-acetatepH2.5 followed by immediate centrifugation and neutralisation ofsupernatant with 50 μL of 3 M NaOH.

Samples were analysed on SDS PAGE as shown in FIG. 26. SDS PAGE analysisof samples from polybead experiment. 5 μL of human serum loaded in Lane1, all other lanes 20 μL out of a 1 mL sample loaded. HSA is human serumalbumin. V_(H) is the heavy chain of IgG at ˜50 kDa and V_(L) is thelight chain at ˜25 kDa. The samples were in SDS loading dye with 1 mMDTT and heated for 5 min at 95° C. There is no IgG in the elution fromuntreated beads whereas OMP85 treated beads contained purified IgG inthe elution. Protein A treated beads also had purified IgG but in suchsmall quantities that they are not visible in the gel scan shown above.This clearly demonstrated that OMP85 can bind to polybeads and is highlyfunctional for IgG binding.

Durability of the Protein Coated Surfaces to Washing with Various Agents

In order to examine the durability of surfaces coated with the modifiedOmp proteins we tested the resilience of the coated surfaces to commonlyused washing and cleaning agents. Well plates were coated with ompprotein using the standard protocol and then washed with the cleaningagent followed by immunodetection as described before. In thepreliminary experiment wells coated with OMP203 were washed withdifferent concentrations of SDS for 5 min and detection with anti-FLAGmonoclonal antibody conjugated to alkaline phosphatase was carried out.The results are shown in FIG. 27.

The 0% SDS wells were washed with SDW. All washes carried out intriplicate and data shown is the average of three wells. There is a veryhigh reading of greater than 3 A₄₀₅ units because the reaction with thePNPP substrate solution was allowed to carry on for 15 min. Conclusion:SDS did not remove significant quantities of proteins indicating thatonce the proteins are attached to the plastic surface, they are notdisplaced by strong detergent.

A similar experiment was carried out on wells coated with OMP203 andOMP18 but this time different concentrations of Tween 20 were used. Thedata are shown in FIG. 28. Again the proteins proved resilient againstwashing with Tween 20. Since most standard ELISA protocols requiremultiple detergent washes, the effect of 1-7 cycles of washing wastested. OMP203 coated wells were washed with varying numbers of washesof detergent-containing solutions (Book 59 p44, p55). One set of threewells was washed with water (SDVV) whilst other wells were washed up to7 times with detergent. The data are shown in the FIG. 29.

A variety of other wash conditions was also tested. Plates were coatedwith either OMP18 or OMP203. This time the wells were incubated for 15min at RT with the test wash solution before washing with water andcompleting the detection assay as above. Note that the OMP18 assayrequired the binding of mouse IgG followed by detection with anti-mouseAP conjugate. The results are shown in FIG. 30. Data from immunoassayafter washing with various agents as shown under the X-axis. DMSO isdimethylsulphoxide; Arg—arginine; OG—octylglucoside; EDTA is ethylenediamine tetra acetic acid; Hellmanex™ II was used. Note that untreatedwells were washed only with water. Each data point is the average ofreadings from 3 wells. None of the wash conditions tested could removesignificant quantity of the protein from the surface.

This data demonstrates the resilience of omp proteins bound topolystyrene in the face of washing with harsh agents such asHellmanexII®, strong acids, strong bases, chaotrophs such as urea andarginine and common detergents and solvents. The binding of the OMPproteins to polystyrene is very robust and hard to displace. In order totest the effects of longer-term exposure to washing agents, platescoated with OMP203 were incubated overnight with washing agents andanalysed by immunoassay with anti-FLAG-AP conjugate. The results areshown in the FIG. 31.

The readings were again very high and above the saturation limit for theplate reader. However, compared to previous data there is a greaterdegree of variation between wells and the 3M NaOH soak has a markedlyreduced signal indicating that 3M NaOH soak has removed or destroyedsurface bound protein. Nevertheless, the surface bound OMP203 proteindemonstrated an extraordinary resilience in overnight soak in all theother agents including harsh wash buffers such as neat HellmanexII, 6MGuHCl, 8M urea, 1% TritonX100.

Enhanced Attachment of Cells to Orla Protein Coated Polystyrene

OMP proteins displaying various extra-cellular matrix (ECM) derivedmotifs (see table overleaf) were coated in triplicate wells of aSarstedt hydrophobic 96 well plate using our standard protocol. Theplates were sprayed with 70% ethanol and placed in a cell culturecabinet, after 10 minutes the remaining ethanol was discarded and eachwell was washed with 200 μL Dulbecco's Phosphate buffered saline. MG63human osteosarcoma cells were harvested from a 75 cm² cell culture flaskusing trypsin and seeded onto the protein coated wells, 200 μL cellsuspension containing 1×10⁴ cells per mL was added to each well. Thecells were incubated overnight in a humidified cell culture incubator at37° C.

TABLE 6 Details of the proteins tested with MG63 cells, all the proteinsare based on the OMP154 protein with insertions of different sizes inthe same elongated loop. Protein Motif No. of Amino acids Source ofmotif OMP154 Control protein 0 N/A OMP153 RGDS 4 Fibronectin OMP162IKVAV 5 Laminin α1 OMP164 PHSRN 5 Fibronectin OMP203 Variable (CS3) 110Fibronectin domain

After 16 hours incubation the number of attached cells in each well wasassessed using an acid phosphatase assay. In this assay the cells aredisrupted with an acidic buffer containing detergent this exposes theacid phosphatase within the cells, the enzyme converts colourlesspara-nitrophenylphosphate (Pnpp) to the yellow compoundpara-nitrophenol. More cells in a well will cause an increase in theconversion of Pnpp to para-nitrophenol which can be easily be detectedby measuring the absorbance of light at 405 nm.

The media was removed from each well and 100 μL 0.1M sodium acetate pH5containing 0.1% Triton X-100 and 1 mg/mL Pnpp was added to each well.The plate was wrapped in aluminium foil and incubated at 37° C. for 2hours. The reaction was terminated by the addition 10 μL 1M NaOH to eachwell. 85 μL solution from each well was transferred to a new 96 wellplate and the absorbance at 405 nm was measured using a plate reader(Book 58 pp 10-25).

FIG. 32 shows the results of culture of MG63 cells on polystyrene coatedwith Orla proteins displaying various ECM motifs.

Conclusions; OMP proteins displaying ECM motifs of different sizes andfrom different ECM proteins are able to increase the number of attachedMG63 cells compared to wells coated with the control OMP154 protein.

Protein Functionalisation of 3D Polystyrene

The standard polystyrene coating protocol used for polystyrene platescan be adapted to protein coat other polystyrene materials such as the3D cell culture material Alvetex, trademark of Reinnervate Ltd. (seeFIG. 33)

Protein concentration used was raised from 1.6 μM to 15 μM toaccommodate the increased surface area of the Alvetex (Book 52 pp137-141). Three samples of Alvetex were treated with control ompAprotein, three were treated with IgG binding protein OMP85. The treatedsamples were washed twice with 2 mL Tris Buffered Saline containing0.05% Tween 20 (TBS-T). Alkaline phosphatase conjugated anti-mouse IgGwas diluted 1:10,000 in TBS-T, 500 μL of diluted antibody was added toeach Alvetex sample and incubated at room temperature for 1 hour. Eachsample was washed twice with 500 μL TBS-T before adding 600 μLPara-nitrophenylphosphate (Pnpp) reagent. After 10 minutes the 1 mL Pnppreagent was removed from each well and the absorbance at 405 nm wasmeasured with a spectrophotometer.

FIG. 34: Detection of alkaline phosphatase conjugated IgG on 3Dpolystyrene treated with OMP proteins.

Conclusion: Treating 3D polystyrene with OMP85 increases the binding ofIgG compared to surfaces coated with the control ompA protein.

OMP proteins can be used to functionalise many different formats ofpolystyrene; 2D plates and flasks, beads and 3D structures.

Protein Attachment to Poly (Lactic Acid)

Most of the work to date has examined the use ompA proteins on variousformats of polystyrene. The same method for protein attachment can beused to protein coat other materials such as poly lactic acid (PLA). Inthis example OMP5, ompA displaying the FLAG epitope, was immobilize on3D printed PLA 3 mm×8 mm scaffolds using the same dilution method usedfor polystyrene (Book 58 pp 28-53).

FIG. 6 shows the cross hatch structure of the 3D printed 2 mm×8 mm PLAdiscs.

Eighteen PLA discs were treated with OMP5, ompA modified to display theFLAG epitope, this can easily be detected using an anti-FLAG antibody. A32 μM solution of OMP5 was prepared, 37.5 μL protein and 562.5 μLphosphate buffered saline was added to each PLA disc. The discs wereincubated overnight at 4-8° C., the following day they were washed threetimes with 500 μL sterile deionized water. The discs were split into sixgroups of three, each group was soaked in a 1% solution of Triton X-100at 37° C. for a different number of days.

-   -   No treatment with Triton X-100    -   1 day in 1% Triton X-100    -   2 days in 1% Triton X-100    -   3 days in 1% Triton X-100    -   4 days in 1% Triton X-100    -   7 days in 1% Triton X-100

At each time point the 1% Triton X-100 solution was removed and replacedin all samples to prevent the reattachment of any protein removed fromthe samples.

At the end timepoint all discs were washed with 500 μL TBS-T thenincubated in 500 μL containing 1 μL per mL M2 alkaline phosphataseconjugated anti-FLAG IgG for 30 minutes at room temperature. Each diskwas washed three times with 500 μL TBS-T then transferred to a new 48well plate. 500 μL Pnpp reagent was added to each disk, after 10 minutesat room temperature the reaction was terminated by the addition of 500μL 1M NaOH.

200 μL Pnpp reagent was removed from each disc and placed into a 96 wellplate, the absorbance at 405 nm of all the samples was measured using aplate reader.

FIG. 35 shows antibody detection of the OMP proteins on PLA afterseveral days immersion 1% triton X-100.

Conclusion: Treating PLA with OMP5 increases the binding of M2 anti-FLAGantibody to the PLA.

Soaking OMP5 treated PLA in 1% triton X-100 for 1 day decreases thebinding of M2 anti-FLAG antibody to the PLA. Soaking the PLA in 1%triton X-100 for any longer does not further reduce the antibodybinding.

Pre-Dilution of Protein

The method for binding of the omp scaffold to plastic surfaces reliesupon the dilution of detergent. The standard protocols require dilutionin situ i.e. the diluent is added to the surface first and then theprotein solution is added to the diluent. This two-step process isdifficult to achieve with precision for some techniques such asmicrodroplet or nanodroplet patterning. In this case it would bedesirable to pre-dilute ex situ and apply to surface as a singledroplet. We know that denatured omp protein cannot be directly dilutedinto detergent-free buffers because they precipitate and drop out ofsolution.

However, the effect of dilution of the refolded protein stored indetergent is not known. A series of experiments to test the effect ofpre-dilution and short term storage were carried out.

a) Dynamic Light Scattering

A solution of 0.1 mg/mL of protein omp208 was prepared in PBS with 2×CMC(0.3 mM) of DM (dodecylmaltoside). The average particle size of theprotein in this solution was determined to be 7.9 nm (±0.9 nm) bydynamic light scattering measurement on a Malvern Zetasizer-nanoinstrument.

Then a 20× dilution of 2 mg/mL solution of omp208 was made into acuvette containing PBS and the average particle size was monitored overthe course of 1 h. The experiment was carried out twice and threereadings were taken at each time point. The data are shown in FIG. 36.

FIG. 36 shows data from the dynamic light scattering experiments. Theplot shows the change in average particle size over the course of 1hour.

The data shows that after dilution the particle size increase from ˜8 nmto 45-55 nm but thereafter was stable at this level for 1 h. These dataindicate that there is some aggregation immediately after dilution butthe aggregates are at a steady state of 45-55 nm for at least 1 h.

b) Immunoassay after Pre-Dilution

We tested whether pre-dilution affects the physisorption of the ompprotein to plastic surface. A dilution of omp203 was made: 2 μM omp203,0.1×CMC of DM in PBS. Immediately after dilution 200 μL of this wereadded to 3 wells of a 96-well untreated polystyrene plate (Time 0). Thenat hourly intervals for up to 6 h, 200 μL samples were withdrawn fromthe pre-diluted solution and added to wells on the same plate, each timein triplicate. At 6 h a control set of wells was also prepared where theprotein was diluted directly into the well as per standard protocol(this was plotted as the −1 sample in the graph of FIG. 38). FIG. 37shows the result of immunoassay of omp203 detection after pre-dilution.The data shows that the ability of the protein to bind to plastics afterpre-dilution remains unimpaired for at least 6 h.

TABLE 7 Protein Name Insertion details OMP0 OMP0 is the originalgold-binding modified version of OmpA comprising truncated N- andC-termini, a 6xHis tag for affinity purification and a cysteine atresidue 10, at the ‘foot’ of the protein for covalent bonding to gold.FIG. 13 OMP5 OMPA comprising a FLAG epitope (DYKDDDDK) in extracellularloop 1. OMP9 Modified version of OMP0. Shown in FIG. 1; comprises allextracellular loops, cysteine residue at residue 10 for gold binding;circularly permutated N and C termini and shortened N terminus OMP13OMP9 with different endpoint N- and C-termini i.e. they are circularlypermuted at different end points (FIG. 16). OMP14 OMP9 with differentendpoint N- and C-termini i.e. they are circularly permuted at differentend points (FIG. 17). OMP18 Tandem repeat of two IgG binding B domainsof SPA fused to N terminus of OMP9 OMP36 OMP0 comprising the YIGSR motiffrom laminin in extracellular loop 1. OMP59 OMP59 is OMP9 with analpha-helical spacer, is shown in FIG. 11 OMP90 OMP90 comprises FGF1 inan OMP59 scaffold OMP128 OMP128 comprises FGF 2 in an OMP59 scaffoldOMP140 OMP9 with loops eliminated; His tag moved to C terminus. OMP153154 with RGDS in long loop Omp154 Modified version of OMP0. 3 truncatedextracellular loops; loop 1 modified with a PT linker and lengthenedwith hydrophilic amino acids (See FIG. 14) OMP162 154 with IKVAV fromlaminin α1 in long loop OMP163 154 with YIGSR from laminin β1 in longloop OMP164 154 with 2xPHSRN in long loop OMP165 154 with Collagen IV-MNYYSNS in long loop pOMP167 Human epidermal growth factor in OMP140OMP170 OMP171 lacking the alpha helical spacer is referred to herein asOMP170. OMP171 OMP9 with all extracellular loops truncated; the Nterminus modified to include an alpha helical spacer sequence (mutatedform of the S. aureus Protein A B domain which does not bind to IgG (thesequence of which is disclosed in Kim et al. (2010) Journal ofexperimental medicine Vol. 207 p 1863-1870) OMP173 A modified version ofOMP171 wherein a protein (HIV antigen p24) is fused to the spacer.OMP174 154 with two FHRRIKA motifs from collagen in tandem in long loopOMP175 154 with IPKASSVPTELSAISMLYLDENEKVVLK from human BMP2 protein inlong loop OMP176 154 with PQVTRGDVFTMP from human vitronectin in longloop OMP177 154 with KKQRFRHRNRKGYSRQ from human vitronectin in longloop OMP178 154 with VDTYDGRGDSVVYGLRSKSKKFRR from human osteopontin inlong loop OMP179 154 with VFDNFVLK motif from human Tenascin-C in longloop pOMP180 Human Leukaemia Inhibitory Factor (LIF). Amino acids 23 to20 of P15081 in UniProt. Isoform 1. fused to N-terminus of OMP140pOMP181 Human fibroblast growth factor 4 (FGF-4). Amino acids 31-206 ofP08620 in UniProt. Isoform 1. fused to N-terminus of OMP140 pOMP182Human Interleukin-4 (IL-4). Amino acids 25-153 of P05112, Isoform 1.fused to N-terminus of OMP140 pOMP183 Human stem cell factor (SCF).Amino acids 26-190 of P21583 (also known as ‘Soluble Kit ligand’ fusedto N-terminus of OMP140 pOMP184 Human Sonic Hedge Hog (Shh). Amino acids24-197 of Q15465 fused to N-terminus of OMP140 OMP185 154 with CollagenI GTPGPQGIAGQRVV motif in long loop OMP186 154 with Hiv TATSYGRKKRRQRRRAHQ motif in long loop OMP187 154 with VQLRNGFPYFSY fromlaminin α2 in long loop OMP188 154 with GLLFYMARINHA from laminin α2 inlong loop OMP189 154 with IKVSV from laminin α2 in long loop pOMP190Human granular macrophage colony stimulating factor (GM-CSF). Aminoacids 18-144 of P04141 fused to N-terminus of OMP140 pOMP191 Humaninterleukin 3 (IL-3). Amino acids 20-152 of P08700 fused to N- terminusof OMP140 pOMP192 Human Thrombopoeitin (TPO). Amino acids 23-195 ofP40225 fused to N-terminus of OMP140 OMP203 Variable (CS3) domain

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of them mean “including but notlimited to”, and they are not intended to (and do not) exclude othermoieties, additives, components, integers or steps. Throughout thedescription and claims of this specification, the singular encompassesthe plural unless the context otherwise requires. In particular, wherethe indefinite article is used, the specification is to be understood ascontemplating plurality as well as singularity, unless the contextrequires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith. All of the features disclosed in this specification(including any accompanying claims, abstract and drawings), and/or allof the steps of any method or process so disclosed, may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. The invention is notrestricted to the details of any foregoing embodiments. The inventionextends to any novel one, or any novel combination, of the featuresdisclosed in this specification (including any accompanying claims,abstract and drawings), or to any novel one, or any novel combination,of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

1-104. (canceled)
 105. A method for immobilising a membrane spanningprotein onto a polymeric substrate, the method comprising: i) providinga sample of a membrane spanning protein in detergent; ii) providing apolymeric substrate; iii) incubating the protein sample of i) with thepolymeric substrate of ii); and iv) reducing the detergent concentrationof the protein sample to 1× Critical Micelle Concentration (CMC) of thedetergent or below; and optionally v) washing and/or sterilising thesubstrate wherein the protein becomes immobilised upon the substrate byphysisorption.
 106. A method according to claim 105 wherein thedetergent concentration is reduced to 0.05×CMC to 1×CMC, preferably to0.05×CMC to 0.7×CMC, preferably to 0.05×CMC to 0.3×CMC.
 107. A methodaccording to claim 105, wherein the membrane spanning protein mayanchor, or may be modified to anchor, a heterologous protein or peptidefor display, wherein an anchored peptide and/or protein is spatiallyremoved from the surface of the polymeric substrate.
 108. A methodaccording to claim 105 wherein the membrane spanning protein: i)comprises a heterologous peptide and/or protein in a loop at a head ofthe protein or in a long loop between membrane spanning strands; ii)comprises a heterologous peptide and/or protein at an N and/or Cterminus at a head of the protein; iii) comprises a heterologous peptideand/or protein at an engineered N and/or C terminus at the head of theprotein; and/or iv) comprises a heterologous peptide and/or protein atan engineered N and/or C terminus at the head of the protein or in oneor more loops provided at a head of the protein; and/or v) the N and/orC terminus of the membrane spanning protein are modified by circularpermutation; and optionally the membrane spanning protein is furtherengineered to: i) remove large internal or external domains which arenot integral to the membrane; ii) truncate one or more loops; and/oriii) elongate one or more loops, for example with hydrophilic spacers toallow the insertion and display of proteins on the loops.
 109. A methodaccording to claim 105 wherein the membrane spanning protein isengineered for an N and/or C terminus to be provided i) in place of aloop; ii) adjacent to a loop; or iii) from within a loop, preferably inthe same loop.
 110. A method according to claim 109 wherein the membranespanning protein is an Outer Membrane Protein A, and the loop is loop 1,3 or
 4. 111. A method according to claim 105 wherein the membranespanning protein comprises a spacer to create a spatial distance betweenthe membrane spanning protein and the peptide and/or protein fordisplay, preferably wherein the spacer is heterologous to the membranespanning protein and/or to the peptide and/or protein.
 112. A methodaccording to claim 111 wherein a spacer is hydrophilic, rigid or semirigid, and preferably comprises an alpha helix, or a PT linker, or aglycine-serine spacer linker.
 113. A method according to claim 105wherein the membrane spanning protein is i) an integral membraneprotein, preferably an ion-channel, preferably a beta-barrel protein,preferably a porin; and/or ii) is eukaryotic, for example plant-derived,animal or mammalian; or prokaryotic, for example bacterial.
 114. Amethod according to claim 113 wherein the membrane spanning protein isan Outer Membrane Proteins (OMP) of Gram-negative bacteria, preferablyOmpA.
 115. A method according to claim 113 wherein the membrane spanningprotein is selected from the group consisting of: i) OmpA modified tocomprise 3 truncated extracellular loops, wherein Loop 1 is retained andcomprises a PT linker and optionally hydrophilic amino acids; ii) OMP154or a variant thereof as listed in Table 3; iii) a membrane spanningprotein comprising a FLAG epitope (DYKDDDDK) in extracellular loop 1;iv) a membrane spanning protein comprising a YIGSR motif from laminin inextracellular loop
 1. 116. A method according to claim 113 wherein themembrane spanning protein is OmpA modified to comprise i) allextracellular loops truncated; ii) the N and C termini positioned on theextracellular end (head) of the protein; iii) a cysteine residue toenable binding of the protein to a gold surface, and optionally an alphahelical spacer at a terminus, preferably the N terminus, and furtheroptionally a heterologous protein or peptide fused to the spacer.
 117. Amethod according to claim 113 wherein the membrane spanning protein isOmpA modified to comprise i) all extracellular loops truncated; ii) theN and C termini positioned on the extracellular end (head) of theprotein; iii) the N terminus modified to include an alpha helical spacersequence; iv) a His tag provided on the C terminus, v) free of cysteineresidues, and preferably wherein the membrane spanning protein is OMP140or a variant thereof as listed in Table 4, or OMP90 and 128 whichcomprise FGF1 and 2 respectively.
 118. A method according to claim 113wherein the membrane spanning protein is OmpA modified to comprise i)the N and C termini positioned on the extracellular end (head) of theprotein; iii) the N terminus truncated and fused to the IgG bindingdomain of Protein A of Staphylococcus aureus; preferably wherein themembrane spanning protein is OMP18.
 119. A method according to claim 105wherein the membrane spanning protein is OmpA encoded the nucleic acidsequence of FIG.
 14. 120. A method according to claim 105 wherein thesubstrate is selected from the group consisting of a mesh, fibres,beads, knitted or woven fabric, micro-well plates, array, or tissueculture flasks and/or the polymer is plastic, silk and otherproteinaceous fibres (for example hair, fur (keratin filaments), actinfilaments, collagen filaments etc.), and graphene, wherein when thepolymer is plastic it is selected from polyvinyl, polyethylene (PE)including for example polyethylene terephthalate (PET) and high-densitypolyethylene (HDPE) and low-density polyethylene (LDPE), polyacrylate(acrylic), polystyrene (PS) including high impact polystyrene (HIPS),silicone, polyester (for example polylactic acid (PLA) or polylacticcoglycolic acid (PGLA)), polyurethane, polypropylene (PP), polyamide(nylon), Acrylonitrile butadiene styrene (ABS),Polyethylene/Acrylonitrile Butadiene Styrene (PE/ABS), bakelite, rubber,latex, polycarbonate (PC), Polycarbonate/Acrylonitrile Butadiene Styrene(PC/ABS) and polyvinyl chloride including for example polyvinylidenechloride (PVDC).
 121. A method according to claim 105, wherein stepsiii) and iv) comprise either I) adding a diluent to the polymericsubstrate such that upon addition of protein sample there is provided aCMC of 1× or below; and incubating the protein sample of i) with thepolymeric substrate of ii); or II) reducing the detergent concentrationof the protein sample such that when incubated with the substrate theCMC is 1× or below; and incubating the protein sample of i) with thepolymeric substrate of ii).
 122. A polymeric substrate comprising amembrane spanning protein immobilised thereon, wherein the membranespanning protein is immobilised upon the substrate by physisorption, andwherein the membrane spanning protein anchors, or is modified to anchor,a heterologous protein or peptide for display, preferably wherein themembrane spanning protein is as defined in claim 107, and/or thesubstrate is as defined in claim
 120. 123. A product comprising apolymeric substrate according to claim 122, preferably wherein theproduct is selected from the group consisting of micro-well plates,tissue culture flasks or plates, plastic beads, fibres, mesh substrates,medical devices such as surgical implants, micro- or nano-particles ofpolymers.
 124. A method of binding a component in a sample or mediatingan interaction of an anchored peptide and/or protein with a component ina sample, the method comprising: i) providing a polymeric substrateaccording to claim 120; ii) adding sample to the substrate; iii)maintaining the substrate with sample under conditions to allow bindingor interaction of any component with anchored protein or peptide of thesubstrate; and optionally iv) removing the sample from the substrate andpurifying any component therefrom, or detecting the presence of anycomponent.
 125. A method according to claim 124, wherein the method isi) a screening assay for a component of interest, further comprising thestep of washing the substrate to remove any unbound material or ii) amethod is for immobilisation of a component of interest from a sample,further comprising the step of detecting the presence or absence of abound component, or iii) a purification method for a component ofinterest from a sample, further comprising eluting any bound component,for example by salt elution, elution by pH change, or competitorbinding.
 126. A method according to claim 125 wherein the membranespanning protein is OMP OMP153, 154, 162-165, 167, 174-179, and 180-192(Tables 3 and 4).
 127. A method according to claim 124, forimmobilisation of Fc tagged proteins, preferably wherein the peptideand/or protein is, or comprises an Fc binding domain, preferably aProtein A, G or L Fc binding domain.
 128. An incubation comprising apolymeric substrate, a membrane spanning protein, and detergent at aconcentration of 1×CMC or below, preferably wherein the membranespanning protein is as defined in claim 107, and/or the substrate is asdefined in claim
 120. 129. A kit comprising a polymeric substrateaccording to claim 120, and a membrane spanning protein as defined inclaim 107, and optionally a chart providing dilution factors to enablephysisorption of a membrane spanning protein to a polymeric substrate,diluents, buffers, substrate, immunoglobulin and binding reagents. 130.A membrane spanning protein according to claim 107 or a nucleic acidsequence encoding a membrane spanning protein according to claim 107.131. A recombinant host cell comprising a nucleic acid sequence orgenetic construct as defined in claim 130.